[display] Loop on the reader's step in display drivers and cap mipi_spi args in the reader

The bool API cost flash at every call site (about 10 B per mipi_spi
instantiation on ESP8266); the unscoped enum keeps the old code shape and
lets callers loop with while (auto step = reader.next(entry)).

AGENTS.md

@@ -216,10 +216,9 @@ file does, and it is the authority when they disagree. The most useful starting
         the helper's arguments instead of writing a loop. 7-byte BCD RTC calendars use `time::decode_bcd_calendar<LAYOUT>`
         and `encode_bcd_calendar<LAYOUT>` with `EPSON_BCD_CALENDAR`, `DS_BCD_CALENDAR` or `PCF_BCD_CALENDAR`.
     *   **Bus helpers:** UART drains with `read_available(on_byte)` and `discard_available()`, text lines with
-        `LineReader<N>`, fixed-length binary frames with `FrameReader<N, HEADER...>`; I2C has `update_register`,
-        `write_registers` (PROGMEM `I2CRegValue` table), `check_chip_id` and `read_bytes_16_le`.
-        `if (!this->status_comm_result(ok)) return;` sets or clears the warning. A child sensor that skips repeated
-        values is `SUB_SENSOR_WITH_DEDUP(name, type)`.
+        `LineReader<N>`; I2C has `update_register`, `write_registers` (PROGMEM `I2CRegValue` table), `check_chip_id`
+        and `read_bytes_16_le`. `if (!this->status_comm_result(ok)) return;` sets or clears the warning.
+        A child sensor that skips repeated values is `SUB_SENSOR_WITH_DEDUP(name, type)`.
     *   **An unset float is `NAN`**, not `optional<float>`; the optional costs 4 to 8 bytes of padding per member.
     *   **`PollingComponent` first runs `update()`** after a random share of the interval; call `this->update()` at the
         end of `setup()` when the entities need a state at boot.

esphome/components/dfrobot_sen0465_uart/dfrobot_sen0465_uart.cpp

@@ -1,7 +1,10 @@
 #include "dfrobot_sen0465_uart.h"
 
+#include <algorithm>
+
 namespace esphome::dfrobot_sen0465_uart {
 
+using dfrobot_sen0465_base::FRAME_HEAD;
 using dfrobot_sen0465_base::FRAME_SIZE;
 using dfrobot_sen0465_base::RESPONSE_TIMEOUT_ID;
 
@@ -15,21 +18,30 @@ void DFRobotSEN0465UARTComponent::setup() {
 }
 
 void DFRobotSEN0465UARTComponent::loop() {
-  // The tail of a reading the probe sent on its own may precede the answer; the reader skips to the frame head.
-  const uint8_t *frame = nullptr;
-  this->read_available<FRAME_SIZE>([&](uint8_t c) { return (frame = this->reader_.feed(c)) == nullptr; });
-  if (frame == nullptr)
+  // The tail of a reading the probe sent on its own may precede the answer; start at the next frame head.
+  uint8_t byte;
+  while (this->rx_count_ == 0 && this->peek_byte(&byte) && byte != FRAME_HEAD)
+    this->read_byte(&byte);
+  const size_t available = this->available();
+  if (available == 0)
+    return;
+  const size_t len = std::min<size_t>(available, FRAME_SIZE - this->rx_count_);
+  if (!this->read_array(this->rx_buffer_ + this->rx_count_, len))
+    return;
+  this->rx_count_ += len;
+  if (this->rx_count_ < FRAME_SIZE)
     return;
 
+  this->rx_count_ = 0;
   this->cancel_timeout(RESPONSE_TIMEOUT_ID);
   this->disable_loop();
-  this->handle_response_(frame);
+  this->handle_response_(this->rx_buffer_);
 }
 
 bool DFRobotSEN0465UARTComponent::write_frame(const uint8_t *frame) {
   // Drop anything left over, such as the answer to the mode change or readings sent before passive mode was set
   this->discard_available();
-  this->reader_.reset();
+  this->rx_count_ = 0;
   this->write_array(frame, FRAME_SIZE);
   return true;
 }
@@ -38,7 +50,7 @@ void DFRobotSEN0465UARTComponent::read_response() {
   this->enable_loop();
   this->set_timeout(RESPONSE_TIMEOUT_ID, RESPONSE_TIMEOUT_MS, [this]() {
     this->disable_loop();
-    this->reader_.reset();
+    this->rx_count_ = 0;
     this->handle_no_response_();
   });
 }

esphome/components/dfrobot_sen0465_uart/dfrobot_sen0465_uart.h

@@ -2,7 +2,6 @@
 
 #include "esphome/components/dfrobot_sen0465_base/dfrobot_sen0465_base.h"
 #include "esphome/components/uart/uart.h"
-#include "esphome/core/frame_reader.h"
 
 namespace esphome::dfrobot_sen0465_uart {
 
@@ -18,7 +17,8 @@ class DFRobotSEN0465UARTComponent final : public dfrobot_sen0465_base::DFRobotSE
   bool write_frame(const uint8_t *frame) override;
   void read_response() override;
 
-  FrameReader<dfrobot_sen0465_base::FRAME_SIZE, dfrobot_sen0465_base::FRAME_HEAD> reader_;
+  uint8_t rx_buffer_[dfrobot_sen0465_base::FRAME_SIZE];
+  uint8_t rx_count_{0};
 };
 
 }  // namespace esphome::dfrobot_sen0465_uart

esphome/components/display/__init__.py

@@ -181,6 +181,16 @@ def get_all_display_metadata() -> dict[str, DisplayMetaData]:
     return {id_.id: meta for id_, meta in entries}
 
 
+def config_has_writer(config: ConfigType) -> bool:
+    """Return True when the display config draws anything."""
+    return (
+        config.get(CONF_AUTO_CLEAR_ENABLED) is True
+        or config.get(CONF_PAGES) is not None
+        or config.get(CONF_LAMBDA) is not None
+        or config.get(CONF_SHOW_TEST_CARD) is True
+    )
+
+
 def get_display_metadata(display_id: ID) -> DisplayMetaData:
     """Get display metadata by ID object
 
@@ -210,10 +220,7 @@ def get_display_metadata(display_id: ID) -> DisplayMetaData:
         height=dimensions[1],
         has_hardware_rotation=False,
         byte_order=disp_config.get(CONF_BYTE_ORDER, cv.UNDEFINED),
-        has_writer=disp_config.get(CONF_AUTO_CLEAR_ENABLED) is True
-        or disp_config.get(CONF_PAGES) is not None
-        or disp_config.get(CONF_LAMBDA) is not None
-        or disp_config.get(CONF_SHOW_TEST_CARD) is True,
+        has_writer=config_has_writer(disp_config),
         rotation=disp_config.get(CONF_ROTATION, 0),
         draw_rounding=disp_config.get(CONF_DRAW_ROUNDING, 0),
     )

esphome/components/display/init_sequence.cpp

@@ -0,0 +1,28 @@
+#include "init_sequence.h"
+#include "esphome/core/hal.h"
+
+namespace esphome::display {
+
+InitSequenceStep InitSequenceReader::next(InitSequenceEntry &entry, uint8_t max_count) {
+  const size_t remaining = this->length_ - this->index_;
+  if (remaining == 0)
+    return INIT_SEQUENCE_STEP_END;
+  const uint8_t *pos = this->sequence_ + this->index_;
+  if (remaining >= 2) {
+    entry.value = progmem_read_byte(pos);
+    entry.count = progmem_read_byte(pos + 1);
+    entry.args = pos + 2;
+    if (entry.count == INIT_SEQUENCE_DELAY_FLAG) {
+      this->index_ += 2;
+      return INIT_SEQUENCE_STEP_DELAY;
+    }
+    if (entry.count <= max_count && remaining - 2 >= entry.count) {
+      this->index_ += 2 + entry.count;
+      return INIT_SEQUENCE_STEP_COMMAND;
+    }
+  }
+  this->index_ = this->length_;
+  return INIT_SEQUENCE_STEP_MALFORMED;
+}
+
+}  // namespace esphome::display

esphome/components/display/init_sequence.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+
+namespace esphome::display {
+
+/// Count byte that marks a delay entry: the byte before it is the delay in ms.
+static constexpr uint8_t INIT_SEQUENCE_DELAY_FLAG = 0xFF;
+
+/// Unscoped so `while (auto step = reader.next(entry))` stops at END.
+enum InitSequenceStep : uint8_t {
+  INIT_SEQUENCE_STEP_END = 0,
+  INIT_SEQUENCE_STEP_COMMAND,
+  INIT_SEQUENCE_STEP_DELAY,
+  INIT_SEQUENCE_STEP_MALFORMED,
+};
+
+/// `value` is the command or the delay in ms; `args` points into the (possibly PROGMEM) sequence.
+struct InitSequenceEntry {
+  const uint8_t *args;
+  uint8_t value;
+  uint8_t count;
+};
+
+/// Walks a mipi.flatten_sequence table (`cmd, count, args...` or `ms, 0xFF`) with progmem reads; resumable.
+class InitSequenceReader {
+ public:
+  InitSequenceReader(const uint8_t *sequence, size_t length) : sequence_(sequence), length_(length) {}
+
+  /// Fill `entry` with the next entry; a command with more than `max_count` args is MALFORMED.
+  InitSequenceStep next(InitSequenceEntry &entry, uint8_t max_count = 0xFE);
+
+ protected:
+  const uint8_t *sequence_;
+  size_t length_;
+  size_t index_{0};
+};
+
+}  // namespace esphome::display

esphome/components/ds1603l/ds1603l.cpp

@@ -1,5 +1,7 @@
 #include "ds1603l.h"
 
+#include <cstring>
+
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 
@@ -8,28 +10,35 @@ namespace esphome::ds1603l {
 ESPHOME_LOG_TAG(TAG, "ds1603l.sensor");
 
 void DS1603L::loop() {
-  this->read_available([this](uint8_t byte) {
-    const uint8_t *frame = this->reader_.feed(byte);
-    if (frame == nullptr) {
-      if (this->reader_.length() == 0) {
-        ESP_LOGV(TAG, "Skipping byte 0x%02X while looking for header", byte);
-      }
-      return;
+  // Assemble frames one byte at a time so a stream that starts mid-frame can realign
+  uint8_t byte;
+  while (this->available() > 0 && this->read_byte(&byte)) {
+    if (this->rx_count_ == 0 && byte != HEADER_BYTE) {
+      ESP_LOGV(TAG, "Skipping byte 0x%02X while looking for header", byte);
+      continue;
     }
-    if (!this->parse_data_(frame)) {
+
+    this->rx_buffer_[this->rx_count_++] = byte;
+    if (this->rx_count_ < FRAME_SIZE) {
+      continue;
+    }
+
+    if (this->parse_data_()) {
+      this->rx_count_ = 0;
+    } else {
       // The header byte was part of the payload of a misaligned frame, so realign instead of dropping everything
-      this->reader_.resync();
+      this->resync_();
     }
-  });
+  }
 }
 
 void DS1603L::dump_config() { LOG_SENSOR("", "DS1603L", this); }
 
-bool DS1603L::parse_data_(const uint8_t *frame) {
-  uint8_t header = frame[0];
-  uint8_t data_h = frame[1];
-  uint8_t data_l = frame[2];
-  uint8_t checksum = frame[3];
+bool DS1603L::parse_data_() {
+  uint8_t header = this->rx_buffer_[0];
+  uint8_t data_h = this->rx_buffer_[1];
+  uint8_t data_l = this->rx_buffer_[2];
+  uint8_t checksum = this->rx_buffer_[3];
 
   uint8_t computed_checksum = (header + data_h + data_l) & 0xFF;
 
@@ -44,4 +53,16 @@ bool DS1603L::parse_data_(const uint8_t *frame) {
   return true;
 }
 
+void DS1603L::resync_() {
+  // Drop the byte that was treated as the header, then look for the next candidate header in what is left
+  size_t start = 1;
+  while (start < this->rx_count_ && this->rx_buffer_[start] != HEADER_BYTE) {
+    start++;
+  }
+  this->rx_count_ -= start;
+  if (this->rx_count_ > 0) {
+    memmove(this->rx_buffer_, this->rx_buffer_ + start, this->rx_count_);
+  }
+}
+
 }  // namespace esphome::ds1603l

esphome/components/ds1603l/ds1603l.h

@@ -6,7 +6,6 @@
 #include "esphome/components/sensor/sensor.h"
 #include "esphome/components/uart/uart.h"
 #include "esphome/core/component.h"
-#include "esphome/core/frame_reader.h"
 
 namespace esphome::ds1603l {
 
@@ -19,10 +18,13 @@ class DS1603L final : public sensor::Sensor, public Component, public uart::UART
   static constexpr uint8_t HEADER_BYTE = 0xFF;
   static constexpr size_t FRAME_SIZE = 4;
 
-  // Validates the checksum of the frame and publishes it. Returns false if the frame is invalid.
-  bool parse_data_(const uint8_t *frame);
+  // Validates the checksum of the frame in rx_buffer_ and publishes it. Returns false if the frame is invalid.
+  bool parse_data_();
+  // Drops the first buffered byte and realigns the buffer on the next possible header byte.
+  void resync_();
 
-  FrameReader<FRAME_SIZE, HEADER_BYTE> reader_;
+  uint8_t rx_buffer_[FRAME_SIZE];  // Buffer for the frame being assembled
+  size_t rx_count_{0};             // Number of bytes currently in rx_buffer_
 };
 
 }  // namespace esphome::ds1603l

esphome/components/epaper_spi/display.py

@@ -15,7 +15,6 @@ from esphome.components.mipi import (
 import esphome.config_validation as cv
 from esphome.config_validation import update_interval
 from esphome.const import (
-    CONF_AUTO_CLEAR_ENABLED,
     CONF_BUSY_PIN,
     CONF_CS_PIN,
     CONF_DATA_RATE,
@@ -189,10 +188,7 @@ def customise_schema(config):
         height,
         has_hardware_rotation=True,
         byte_order=cv.UNDEFINED,
-        has_writer=config.get(CONF_AUTO_CLEAR_ENABLED) is True
-        or config.get(CONF_PAGES) is not None
-        or config.get(CONF_LAMBDA) is not None
-        or config.get(CONF_SHOW_TEST_CARD) is True,
+        has_writer=display.config_has_writer(config),
         rotation=config.get(CONF_ROTATION, 0),
         draw_rounding=0,
     )

esphome/components/epaper_spi/epaper_spi.cpp

@@ -1,4 +1,5 @@
 #include "epaper_spi.h"
+#include "esphome/components/display/init_sequence.h"
 #include <cinttypes>
 #include "esphome/core/application.h"
 #include "esphome/core/helpers.h"
@@ -315,26 +316,18 @@ void EPaperBase::start_data_() {
 void EPaperBase::on_safe_shutdown() { this->deep_sleep(); }
 
 void EPaperBase::send_init_sequence_(const uint8_t *sequence, size_t length) {
-  size_t index = 0;
-
-  while (index != length) {
-    if (length - index < 2) {
+  display::InitSequenceReader reader(sequence, length);
+  display::InitSequenceEntry entry;
+  while (auto step = reader.next(entry)) {
+    if (step == display::INIT_SEQUENCE_STEP_MALFORMED) {
       this->mark_failed(LOG_STR("Malformed init sequence"));
       return;
     }
-    const uint8_t cmd = sequence[index++];
-    if (const uint8_t x = sequence[index++]; x == DELAY_FLAG) {
-      ESP_LOGV(TAG, "Delay %dms", cmd);
-      delay(cmd);
+    if (step == display::INIT_SEQUENCE_STEP_DELAY) {
+      ESP_LOGV(TAG, "Delay %dms", entry.value);
+      delay(entry.value);
     } else {
-      const uint8_t num_args = x & 0x7F;
-      if (length - index < num_args) {
-        ESP_LOGE(TAG, "Malformed init sequence, cmd = %X, num_args = %u", cmd, num_args);
-        this->mark_failed();
-        return;
-      }
-      this->cmd_data(cmd, sequence + index, num_args);
-      index += num_args;
+      this->cmd_data(entry.value, entry.args, entry.count);
     }
   }
 }

esphome/components/epaper_spi/epaper_spi.h

@@ -34,7 +34,6 @@ static constexpr uint32_t MAX_TRANSFER_TIME = 10;  // Transfer in 10ms blocks to
 static constexpr size_t MAX_TRANSFER_SIZE = 128;
 // Longer busy waits are the waveform or a stuck pin, and are polled at the normal loop pace
 static constexpr uint32_t FAST_BUSY_POLL_MS = 50;
-static constexpr uint8_t DELAY_FLAG = 0xFF;
 
 class EPaperBase : public Display,
                    public spi::SPIDevice<spi::BIT_ORDER_MSB_FIRST, spi::CLOCK_POLARITY_LOW, spi::CLOCK_PHASE_LEADING,

esphome/components/mipi_dsi/display.py

@@ -38,7 +38,6 @@ from esphome.components.mipi import (
 )
 import esphome.config_validation as cv
 from esphome.const import (
-    CONF_AUTO_CLEAR_ENABLED,
     CONF_COLOR_ORDER,
     CONF_DIMENSIONS,
     CONF_ENABLE_PIN,
@@ -167,8 +166,7 @@ def _config_schema(config: ConfigType) -> ConfigType:
         height,
         has_hardware_rotation=False,
         byte_order=config[CONF_BYTE_ORDER],
-        has_writer=requires_buffer(config)
-        or config.get(CONF_AUTO_CLEAR_ENABLED) is True,
+        has_writer=display.config_has_writer(config),
         rotation=config.get(CONF_ROTATION, 0),
         draw_rounding=config.get(CONF_DRAW_ROUNDING, 0),
     )

esphome/components/mipi_dsi/mipi_dsi.cpp

@@ -1,6 +1,7 @@
 #ifdef USE_ESP32_VARIANT_ESP32P4
 #include <utility>
 #include "mipi_dsi.h"
+#include "esphome/components/display/init_sequence.h"
 #include "esphome/core/helpers.h"
 
 #include <algorithm>
@@ -123,47 +124,38 @@ void MipiDsi::setup() {
     this->smark_failed(LOG_STR("esp_lcd_init failed"), err);
     return;
   }
-  size_t index = 0;
-  const uint8_t *seq = this->init_sequence_;
-  const size_t len = this->init_sequence_len_;
-  while (index != len) {
-    if (len - index < 2) {
+  display::InitSequenceReader reader(this->init_sequence_, this->init_sequence_len_);
+  display::InitSequenceEntry entry;
+  while (auto step = reader.next(entry)) {
+    if (step == display::INIT_SEQUENCE_STEP_MALFORMED) {
       this->mark_failed(LOG_STR("Malformed init sequence"));
       return;
     }
-    uint8_t cmd = seq[index++];
-    uint8_t x = seq[index++];
-    if (x == DELAY_FLAG) {
-      ESP_LOGD(TAG, "Delay %dms", cmd);
-      delay(cmd);
-    } else {
-      uint8_t num_args = x & 0x7F;
-      if (len - index < num_args) {
-        this->mark_failed(LOG_STR("Malformed init sequence"));
-        return;
-      }
-      if (cmd == SLEEP_OUT) {
-        // are we ready, boots?
-        int duration = when - millis();
-        if (duration > 0) {
-          delay(duration);
-        }
-      }
-      const auto *ptr = seq + index;
-#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERY_VERBOSE
-      char hex_buf[format_hex_pretty_size(MIPI_DSI_MAX_CMD_LOG_BYTES)];
-#endif
-      ESP_LOGVV(TAG, "Command %02X, length %d, byte(s) %s", cmd, num_args,
-                format_hex_pretty_to(hex_buf, ptr, num_args, '.'));
-      err = esp_lcd_panel_io_tx_param(this->io_handle_, cmd, ptr, num_args);
-      if (err != ESP_OK) {
-        this->smark_failed(LOG_STR("lcd_panel_io_tx_param failed"), err);
-        return;
-      }
-      index += num_args;
-      if (cmd == SLEEP_OUT)
-        delay(10);
+    if (step == display::INIT_SEQUENCE_STEP_DELAY) {
+      ESP_LOGD(TAG, "Delay %dms", entry.value);
+      delay(entry.value);
+      continue;
     }
+    const uint8_t cmd = entry.value;
+    if (cmd == SLEEP_OUT) {
+      // are we ready, boots?
+      int duration = when - millis();
+      if (duration > 0) {
+        delay(duration);
+      }
+    }
+#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERY_VERBOSE
+    char hex_buf[format_hex_pretty_size(MIPI_DSI_MAX_CMD_LOG_BYTES)];
+#endif
+    ESP_LOGVV(TAG, "Command %02X, length %d, byte(s) %s", cmd, entry.count,
+              format_hex_pretty_to(hex_buf, entry.args, entry.count, '.'));
+    err = esp_lcd_panel_io_tx_param(this->io_handle_, cmd, entry.args, entry.count);
+    if (err != ESP_OK) {
+      this->smark_failed(LOG_STR("lcd_panel_io_tx_param failed"), err);
+      return;
+    }
+    if (cmd == SLEEP_OUT)
+      delay(10);
   }
   this->io_lock_ = xSemaphoreCreateBinary();
   esp_lcd_dpi_panel_event_callbacks_t cbs = {

esphome/components/mipi_dsi/mipi_dsi.h

@@ -31,7 +31,6 @@ const uint8_t INVERT_OFF = 0x20;
 const uint8_t INVERT_ON = 0x21;
 const uint8_t DISPLAY_ON = 0x29;
 const uint8_t CMD2_BKSEL = 0xFF;
-const uint8_t DELAY_FLAG = 0xFF;
 const uint8_t MADCTL_BGR = 0x08;
 const uint8_t MADCTL_MX = 0x40;
 const uint8_t MADCTL_MY = 0x80;

esphome/components/mipi_rgb/display.py

@@ -50,7 +50,6 @@ from esphome.components.spi import (
 )
 import esphome.config_validation as cv
 from esphome.const import (
-    CONF_AUTO_CLEAR_ENABLED,
     CONF_BLUE,
     CONF_COLOR_ORDER,
     CONF_CS_PIN,
@@ -243,8 +242,7 @@ def _config_schema(config: ConfigType) -> ConfigType:
         height,
         has_hardware_rotation=True,
         byte_order=config[CONF_BYTE_ORDER],
-        has_writer=requires_buffer(config)
-        or config.get(CONF_AUTO_CLEAR_ENABLED) is True,
+        has_writer=display.config_has_writer(config),
         rotation=config.get(CONF_ROTATION, 0),
         draw_rounding=config.get(CONF_DRAW_ROUNDING, 0),
     )

esphome/components/mipi_rgb/mipi_rgb.cpp

@@ -1,5 +1,6 @@
 #if defined(USE_ESP32_VARIANT_ESP32S3) || defined(USE_ESP32_VARIANT_ESP32P4) || defined(USE_ESP32_VARIANT_ESP32S31)
 #include "mipi_rgb.h"
+#include "esphome/components/display/init_sequence.h"
 #include "esphome/core/gpio.h"
 #include "esphome/core/hal.h"
 #include "esphome/core/helpers.h"
@@ -13,8 +14,6 @@
 
 namespace esphome::mipi_rgb {
 
-static const uint8_t DELAY_FLAG = 0xFF;
-
 // Maximum bytes to log for init commands (truncated if larger)
 static constexpr size_t MIPI_RGB_MAX_CMD_LOG_BYTES = 64;
 static constexpr uint8_t MADCTL_MY = 0x80;     // Bit 7 Bottom to top
@@ -75,44 +74,30 @@ void MipiRgbSpi::write_data_(uint8_t value) {
   this->disable();
 }
 
-/**
- * this relies upon the init sequence being well-formed, which is guaranteed by the Python init code.
- */
-
 void MipiRgbSpi::write_init_sequence_() {
-  size_t index = 0;
-  const uint8_t *seq = this->init_sequence_;
-  const size_t len = this->init_sequence_len_;
-  while (index != len) {
-    if (len - index < 2) {
+  display::InitSequenceReader reader(this->init_sequence_, this->init_sequence_len_);
+  display::InitSequenceEntry entry;
+  while (auto step = reader.next(entry)) {
+    if (step == display::INIT_SEQUENCE_STEP_MALFORMED) {
       this->mark_failed(LOG_STR("Malformed init sequence"));
       return;
     }
-    uint8_t cmd = seq[index++];
-    uint8_t x = seq[index++];
-    if (x == DELAY_FLAG) {
-      ESP_LOGD(TAG, "Delay %dms", cmd);
-      delay(cmd);
-    } else {
-      uint8_t num_args = x & 0x7F;
-      if (len - index < num_args) {
-        this->mark_failed(LOG_STR("Malformed init sequence"));
-        return;
-      }
-      if (cmd == SLEEP_OUT) {
-        delay(120);  // NOLINT
-      }
-      const auto *ptr = seq + index;
-      char hex_buf[format_hex_pretty_size(MIPI_RGB_MAX_CMD_LOG_BYTES)];
-      ESP_LOGD(TAG, "Write command %02X, length %d, byte(s) %s", cmd, num_args,
-               format_hex_pretty_to(hex_buf, ptr, num_args, '.'));
-      index += num_args;
-      this->write_command_(cmd);
-      while (num_args-- != 0)
-        this->write_data_(*ptr++);
-      if (cmd == SLEEP_OUT)
-        delay(10);
+    if (step == display::INIT_SEQUENCE_STEP_DELAY) {
+      ESP_LOGD(TAG, "Delay %dms", entry.value);
+      delay(entry.value);
+      continue;
     }
+    const uint8_t cmd = entry.value;
+    if (cmd == SLEEP_OUT)
+      delay(120);  // NOLINT
+    char hex_buf[format_hex_pretty_size(MIPI_RGB_MAX_CMD_LOG_BYTES)];
+    ESP_LOGD(TAG, "Write command %02X, length %d, byte(s) %s", cmd, entry.count,
+             format_hex_pretty_to(hex_buf, entry.args, entry.count, '.'));
+    this->write_command_(cmd);
+    for (uint8_t i = 0; i < entry.count; i++)
+      this->write_data_(entry.args[i]);
+    if (cmd == SLEEP_OUT)
+      delay(10);
   }
   // this->spi_teardown();  // SPI not needed after this
   delay(10);

esphome/components/mipi_spi/display.py

@@ -33,7 +33,6 @@ from esphome.components.spi import CONF_SPI_MODE, TYPE_OCTAL, TYPE_QUAD, TYPE_SI
 import esphome.config_validation as cv
 from esphome.config_validation import ALLOW_EXTRA
 from esphome.const import (
-    CONF_AUTO_CLEAR_ENABLED,
     CONF_BRIGHTNESS,
     CONF_BUFFER_SIZE,
     CONF_COLOR_ORDER,
@@ -73,6 +72,10 @@ Model = mipi_spi_ns.enum("Model")
 PixelMode = mipi_spi_ns.enum("PixelMode")
 BusType = mipi_spi_ns.enum("BusType")
 
+# Matches INIT_SEQUENCE_MAX_ARGS, the flash copy buffer in mipi_spi.h
+INIT_SEQUENCE_MAX_ARGS = 128
+
+
 COLOR_ORDERS = {
     MODE_RGB: ColorOrder.COLOR_ORDER_RGB,
     MODE_BGR: ColorOrder.COLOR_ORDER_BGR,
@@ -216,7 +219,15 @@ def model_schema(config: ConfigType) -> cv.All | cv.Schema:
                     bus_mode, lower=True
                 ),
                 cv.Required(CONF_MODEL): cv.one_of(model.name, upper=True),
-                iseqconf: cv.ensure_list(map_sequence),
+                iseqconf: cv.ensure_list(
+                    cv.All(
+                        map_sequence,
+                        cv.Length(
+                            max=INIT_SEQUENCE_MAX_ARGS + 1,
+                            msg=f"An init sequence command can have at most {INIT_SEQUENCE_MAX_ARGS} data bytes",
+                        ),
+                    )
+                ),
                 cv.Optional(CONF_BUFFER_SIZE): cv.All(
                     cv.percentage, cv.Range(0.12, 1.0)
                 ),
@@ -290,8 +301,7 @@ def customise_schema(config: ConfigType) -> ConfigType:
         height,
         has_hardware_transform,
         byte_order=config[CONF_BYTE_ORDER],
-        has_writer=requires_buffer(config)
-        or config.get(CONF_AUTO_CLEAR_ENABLED) is True,
+        has_writer=display.config_has_writer(config),
         rotation=config.get(CONF_ROTATION, 0),
         draw_rounding=config.get(CONF_DRAW_ROUNDING, 0),
     )

esphome/components/mipi_spi/mipi_spi.h

@@ -7,12 +7,16 @@
 #include "esphome/components/spi/spi.h"
 #include "esphome/components/display/display.h"
 #include "esphome/components/display/display_color_utils.h"
+#include "esphome/components/display/init_sequence.h"
 #include "esphome/core/hal.h"
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 
 namespace esphome::mipi_spi {
 
+/// Largest argument count in one init command; display.py rejects longer ones.
+static constexpr size_t INIT_SEQUENCE_MAX_ARGS = 128;
+
 ESPHOME_LOG_TAG(TAG, "display.mipi_spi");
 
 // Maximum bytes to log for commands (truncated if larger)
@@ -48,7 +52,6 @@ static constexpr uint8_t MADCTL_XFLIP = 0x02;        // Mirror the display horiz
 static constexpr uint8_t MADCTL_YFLIP = 0x01;        // Mirror the display vertically
 static constexpr uint16_t MADCTL_FLIP_FLAG = 0x100;  // controller uses axis flip bits
 
-static constexpr uint8_t DELAY_FLAG = 0xFF;
 // store a 16 bit value in a buffer, big endian.
 static inline void put16_be(uint8_t *buf, uint16_t value) {
   buf[0] = value >> 8;
@@ -163,36 +166,23 @@ class MipiSpi : public display::Display,
 
     // need to know when the display is ready for SLPOUT command - will be 120ms after reset
     auto when = millis() + 120;
-    size_t index = 0;
-    const uint8_t *seq = this->init_sequence_;
-    const size_t len = this->init_sequence_len_;
-    while (index != len) {
-      if (len - index < 2) {
-        esph_log_e(TAG, "Malformed init sequence");
-        this->mark_failed();
+    display::InitSequenceReader reader(this->init_sequence_, this->init_sequence_len_);
+    display::InitSequenceEntry entry;
+    // The sequence is in flash, which SPI DMA (and ESP8266 byte loads) cannot read
+    uint8_t args[INIT_SEQUENCE_MAX_ARGS];
+    while (auto step = reader.next(entry, sizeof(args))) {
+      if (step == display::INIT_SEQUENCE_STEP_MALFORMED) {
+        this->mark_failed(LOG_STR("Malformed init sequence"));
         return;
       }
-      uint8_t cmd = progmem_read_byte(seq + index++);
-      uint8_t x = progmem_read_byte(seq + index++);
-      if (x == DELAY_FLAG) {
-        if (cmd == 0) {
-          cmd = clamp_at_least((int) (when - millis()), 0);
-        }
-        esph_log_d(TAG, "Delay %dms", cmd);
-        delay(cmd);
-      } else {
-        uint8_t num_args = x & 0x7F;
-        if (len - index < num_args) {
-          esph_log_e(TAG, "Malformed init sequence");
-          this->mark_failed();
-          return;
-        }
-        // The sequence is in flash, which SPI DMA (and ESP8266 byte loads) cannot read
-        uint8_t args[0x80];
-        progmem_memcpy(args, seq + index, num_args);
-        this->write_command_(cmd, args, num_args);
-        index += num_args;
+      if (step == display::INIT_SEQUENCE_STEP_DELAY) {
+        const uint8_t ms = entry.value != 0 ? entry.value : clamp_at_least((int) (when - millis()), 0);
+        esph_log_d(TAG, "Delay %dms", ms);
+        delay(ms);
+        continue;
       }
+      progmem_memcpy(args, entry.args, entry.count);
+      this->write_command_(entry.value, args, entry.count);
     }
     this->reset_params_();
     // Marks init as done, so later commands log at verbose level instead of debug

esphome/components/sm300d2/sm300d2.cpp

@@ -1,27 +1,33 @@
 #include "sm300d2.h"
-#include "esphome/core/frame_reader.h"
 #include "esphome/core/log.h"
 
 namespace esphome::sm300d2 {
 
 ESPHOME_LOG_TAG(TAG, "sm300d2");
-static constexpr uint8_t SM300D2_RESPONSE_LENGTH = 17;
+static const uint8_t SM300D2_RESPONSE_LENGTH = 17;
 
 void SM300D2Sensor::update() {
-  // Takes the first frame already received; only one cut off at the end of the buffer is waited for
-  FrameReader<SM300D2_RESPONSE_LENGTH, 0x3C, 0x02> reader;
-  const uint8_t *response = nullptr;
-  this->read_available<1>([&](uint8_t c) { return (response = reader.feed(c)) == nullptr; });
-  for (uint8_t c; response == nullptr && reader.length() > 0 && this->read_byte(&c);)
-    response = reader.feed(c);
+  uint8_t response[SM300D2_RESPONSE_LENGTH];
+  uint8_t peeked;
 
-  if (response == nullptr) {
+  while (this->available() > 0 && this->peek_byte(&peeked) && peeked != 0x3C)
+    this->read();
+
+  bool read_success = read_array(response, SM300D2_RESPONSE_LENGTH);
+
+  if (!read_success) {
     ESP_LOGW(TAG, "Reading data from SM300D2 failed!");
+    status_set_warning();
+    return;
+  }
+
+  if (response[0] != 0x3C || response[1] != 0x02) {
+    ESP_LOGW(TAG, "Invalid preamble for SM300D2 response!");
     this->status_set_warning();
     return;
   }
 
-  uint16_t calculated_checksum = sum_bytes(response, SM300D2_RESPONSE_LENGTH - 1);
+  uint16_t calculated_checksum = this->sm300d2_checksum_(response);
   // Occasionally the checksum has a +/- 0x80 offset. Negative temperatures are
   // responsible for some of these. The rest are unknown/undocumented.
   if ((calculated_checksum != response[SM300D2_RESPONSE_LENGTH - 1]) &&
@@ -77,6 +83,8 @@ void SM300D2Sensor::update() {
     this->humidity_sensor_->publish_state(humidity);
 }
 
+uint16_t SM300D2Sensor::sm300d2_checksum_(uint8_t *ptr) { return sum_bytes(ptr, SM300D2_RESPONSE_LENGTH - 1); }
+
 void SM300D2Sensor::dump_config() {
   ESP_LOGCONFIG(TAG, "SM300D2:");
   LOG_SENSOR("  ", "CO2", this->co2_sensor_);

esphome/components/sm300d2/sm300d2.h

@@ -20,6 +20,8 @@ class SM300D2Sensor final : public PollingComponent, public uart::UARTDevice {
   void dump_config() override;
 
  protected:
+  uint16_t sm300d2_checksum_(uint8_t *ptr);
+
   sensor::Sensor *co2_sensor_{nullptr};
   sensor::Sensor *formaldehyde_sensor_{nullptr};
   sensor::Sensor *tvoc_sensor_{nullptr};

esphome/components/st7305/display.py

@@ -4,7 +4,6 @@ import pkgutil
 from esphome import pins
 import esphome.codegen as cg
 from esphome.components import display, spi
-from esphome.components.display import CONF_SHOW_TEST_CARD
 from esphome.components.mipi import (
     DriverChip,
     flatten_sequence,
@@ -13,16 +12,13 @@ from esphome.components.mipi import (
 )
 import esphome.config_validation as cv
 from esphome.const import (
-    CONF_AUTO_CLEAR_ENABLED,
     CONF_CS_PIN,
     CONF_DATA_RATE,
     CONF_DC_PIN,
     CONF_HEIGHT,
     CONF_ID,
     CONF_INIT_SEQUENCE,
-    CONF_LAMBDA,
     CONF_MODEL,
-    CONF_PAGES,
     CONF_RESET_PIN,
     CONF_ROTATION,
     CONF_WIDTH,
@@ -182,10 +178,7 @@ def customise_schema(config: ConfigType) -> ConfigType:
         config[CONF_HEIGHT],
         has_hardware_rotation=False,
         byte_order=cv.UNDEFINED,
-        has_writer=config.get(CONF_AUTO_CLEAR_ENABLED) is True
-        or config.get(CONF_PAGES) is not None
-        or config.get(CONF_LAMBDA) is not None
-        or config.get(CONF_SHOW_TEST_CARD) is True,
+        has_writer=display.config_has_writer(config),
         rotation=config.get(CONF_ROTATION, 0),
     )
     return config

esphome/components/st7305/st7305.cpp

@@ -56,33 +56,26 @@ void ST7305::reset_() {
 }
 
 void ST7305::send_init_sequence_() {
-  while (this->init_index_ < this->init_sequence_length_) {
-    if (this->init_sequence_length_ - this->init_index_ < 2) {
-      this->mark_failed(LOG_STR("Malformed init sequence"));
-      return;
-    }
-    const uint8_t command = progmem_read_byte(&this->init_sequence_[this->init_index_++]);
-    const uint8_t count = progmem_read_byte(&this->init_sequence_[this->init_index_++]);
-    if (count == 0xFF) {
-      // Resume the sequence after the delay instead of blocking the main loop.
-      this->set_timeout(STARTUP_TIMEOUT_ID, command, [this]() { this->send_init_sequence_(); });
-      return;
-    }
-    if (this->init_sequence_length_ - this->init_index_ < count) {
-      this->mark_failed(LOG_STR("Malformed init sequence"));
-      return;
-    }
+  display::InitSequenceEntry entry;
+  display::InitSequenceStep step;
+  while ((step = this->init_reader_.next(entry)) == display::INIT_SEQUENCE_STEP_COMMAND) {
     this->enable();
-    this->send_command_(command);
-    if (count != 0) {
+    this->send_command_(entry.value);
+    if (entry.count != 0) {
       this->dc_pin_->digital_write(true);
-      for (uint8_t i = 0; i < count; i++)
-        this->write_byte(progmem_read_byte(&this->init_sequence_[this->init_index_ + i]));
+      for (uint8_t i = 0; i < entry.count; i++)
+        this->write_byte(progmem_read_byte(entry.args + i));
     }
     this->disable();
-    this->init_index_ += count;
   }
-  this->finish_init_();
+  if (step == display::INIT_SEQUENCE_STEP_DELAY) {
+    // Resume the sequence after the delay instead of blocking the main loop.
+    this->set_timeout(STARTUP_TIMEOUT_ID, entry.value, [this]() { this->send_init_sequence_(); });
+  } else if (step == display::INIT_SEQUENCE_STEP_MALFORMED) {
+    this->mark_failed(LOG_STR("Malformed init sequence"));
+  } else {
+    this->finish_init_();
+  }
 }
 
 void ST7305::finish_init_() {

esphome/components/st7305/st7305.h

@@ -4,6 +4,7 @@
 #include <cstdint>
 
 #include "esphome/components/display/display_buffer.h"
+#include "esphome/components/display/init_sequence.h"
 #include "esphome/components/spi/spi.h"
 #include "esphome/core/component.h"
 #include "esphome/core/hal.h"
@@ -35,8 +36,7 @@ class ST7305 : public display::DisplayBuffer,
         row_start_(row_start),
         row_end_(row_end),
         buffer_length_(static_cast<size_t>(width) * static_cast<size_t>(height) / 8),
-        init_sequence_(init_sequence),
-        init_sequence_length_(init_sequence_length) {}
+        init_reader_(init_sequence, init_sequence_length) {}
 
   void setup() override;
   void update() override;
@@ -113,9 +113,7 @@ class ST7305 : public display::DisplayBuffer,
   uint8_t row_start_;
   uint8_t row_end_;
   size_t buffer_length_;
-  const uint8_t *init_sequence_;
-  size_t init_sequence_length_;
-  size_t init_index_{0};
+  display::InitSequenceReader init_reader_;
   bool ready_{false};
 
   int x_low_{0};

esphome/components/ufm01/ufm01.cpp

@@ -44,6 +44,8 @@ static constexpr std::array<uint8_t, 7> GET_SOFTWARE_VERSION = {0xFE, 0xFE, 0x11
 static constexpr size_t FRAME_DEVICE_ID_INDEX = 2;
 static constexpr size_t FRAME_CHECKSUM_INDEX = 30;
 static constexpr size_t FRAME_STOP_INDEX = 31;
+static constexpr uint8_t FRAME_START_BYTE_1 = 0x3C;
+static constexpr uint8_t FRAME_START_BYTE_2 = 0x32;
 static constexpr uint8_t PASSIVE_START_BYTE_2 = 0x64;
 static constexpr uint8_t PASSIVE_START_BYTE_2_WITH_ID = 0x96;
 static constexpr uint8_t FRAME_STOP_BYTE = 0x16;
@@ -118,8 +120,9 @@ static bool check_byte(const uint8_t data[FRAME_SIZE], size_t index, uint8_t exp
 
 static bool validate_active_frame(const uint8_t data[FRAME_SIZE]) {
   const uint8_t sum = sum_bytes(data, FRAME_CHECKSUM_INDEX);
-  // FrameReader already matched the start bytes
-  return check_byte(data, FRAME_INDEX_INSTANT_FLOW_FLAG, FRAME_FLAG_INSTANT_FLOW, "instant flow flag") &&
+  return check_byte(data, 0, FRAME_START_BYTE_1, "start byte 1") &&
+         check_byte(data, 1, FRAME_START_BYTE_2, "start byte 2") &&
+         check_byte(data, FRAME_INDEX_INSTANT_FLOW_FLAG, FRAME_FLAG_INSTANT_FLOW, "instant flow flag") &&
          check_byte(data, FRAME_INDEX_RESERVED_SECTION, FRAME_FLAG_RESERVED_SECTION, "reserved section flag") &&
          check_byte(data, FRAME_INDEX_TEMP_FLAG, FRAME_FLAG_TEMP, "temperature flag") &&
          check_byte(data, FRAME_CHECKSUM_INDEX, sum, "checksum") &&
@@ -212,7 +215,7 @@ static bool read_flow_rate_out_of_range(const uint8_t data[FRAME_SIZE]) {
 
 void UFM01Component::flush_rx_() {
   this->discard_available();
-  this->active_reader_.reset();
+  this->read_index_ = 0;
 }
 
 void UFM01Component::send_command_no_wait_(const std::array<uint8_t, 7> &command) {
@@ -420,7 +423,7 @@ bool UFM01Component::service_software_version_(uint32_t now) {
 }
 #endif  // USE_UFM01_SOFTWARE_VERSION
 
-void UFM01Component::on_active_frame_(const uint8_t data[FRAME_SIZE], uint32_t now) {
+void UFM01Component::on_active_frame_(uint8_t data[FRAME_SIZE], uint32_t now) {
 #ifdef USE_UFM01_METER_ID
   this->publish_meter_id_from_frame_(data);
 #endif
@@ -458,26 +461,40 @@ void UFM01Component::on_active_frame_(const uint8_t data[FRAME_SIZE], uint32_t n
 bool UFM01Component::process_active_stream_(uint32_t now) {
   bool got_valid_frame = false;
 
-  const bool read_ok = this->read_available([this, now, &got_valid_frame](uint8_t byte) {
-    const uint8_t *frame = this->active_reader_.feed(byte);
-    if (frame == nullptr) {
-      if (this->active_reader_.length() == 0) {
-        ESP_LOGD(TAG, "not start of data (is 0x%02X)", byte);
-      }
-      return;
+  while (this->available()) {
+    if (!this->read_byte(&this->data_[this->read_index_])) {
+      ESP_LOGW(TAG, "unable to read byte");
+      this->read_index_ = 0;
+      continue;
     }
-    if (validate_active_frame(frame)) {
-      this->on_active_frame_(frame, now);
+    if ((this->read_index_ == 0 && this->data_[0] != FRAME_START_BYTE_1) ||
+        (this->read_index_ == 1 && this->data_[1] != FRAME_START_BYTE_2)) {
+      ESP_LOGD(TAG, "not start of data at %" PRId32 " (is 0x%02X)", this->read_index_, this->data_[this->read_index_]);
+      this->read_index_ = 0;
+      continue;
+    }
+    if (++this->read_index_ < static_cast<int32_t>(FRAME_SIZE))
+      continue;
+
+    if (validate_active_frame(this->data_)) {
+      this->on_active_frame_(this->data_, now);
+      this->read_index_ = 0;
       got_valid_frame = true;
-      return;
+      continue;
     }
-    log_hex(frame, FRAME_SIZE);
+
+    log_hex(this->data_, sizeof(this->data_));
     ESP_LOGW(TAG, "unable to read data");
-    this->active_reader_.resync();
-  });
-  if (!read_ok) {
-    ESP_LOGW(TAG, "unable to read byte");
-    this->active_reader_.reset();
+    for (int32_t i = 2;
+         i < static_cast<int32_t>(FRAME_STOP_INDEX) && this->read_index_ == static_cast<int32_t>(FRAME_SIZE); ++i) {
+      if ((this->data_[i] == FRAME_START_BYTE_1) && (this->data_[i + 1] == FRAME_START_BYTE_2)) {
+        for (int32_t j = i; j < static_cast<int32_t>(FRAME_SIZE); ++j)
+          this->data_[j - i] = this->data_[j];
+        this->read_index_ = static_cast<int32_t>(FRAME_SIZE) - i;
+      }
+    }
+    if (this->read_index_ == static_cast<int32_t>(FRAME_SIZE))
+      this->read_index_ = 0;
   }
 
   return got_valid_frame;

esphome/components/ufm01/ufm01.h

@@ -2,7 +2,6 @@
 
 #include "esphome/core/component.h"
 #include "esphome/core/defines.h"
-#include "esphome/core/frame_reader.h"
 #ifdef USE_BINARY_SENSOR
 #include "esphome/components/binary_sensor/binary_sensor.h"
 #endif
@@ -26,8 +25,6 @@ class TestableUFM01;
 }  // namespace testing
 
 static constexpr size_t FRAME_SIZE = 32;
-static constexpr uint8_t FRAME_START_BYTE_1 = 0x3C;
-static constexpr uint8_t FRAME_START_BYTE_2 = 0x32;
 static constexpr size_t PASSIVE_FRAME_SIZE = 23;
 static constexpr size_t PASSIVE_FRAME_WITH_ID_SIZE = 39;
 #ifdef USE_UFM01_METER_ID
@@ -111,7 +108,7 @@ class UFM01Component : public uart::UARTDevice, public Component {
   bool consume_ack_();
   void flush_rx_();
   bool process_active_stream_(uint32_t now);
-  void on_active_frame_(const uint8_t data[FRAME_SIZE], uint32_t now);
+  void on_active_frame_(uint8_t data[FRAME_SIZE], uint32_t now);
 #ifdef USE_UFM01_METER_ID
   void publish_meter_id_from_frame_(const uint8_t data[FRAME_SIZE]);
 #endif
@@ -148,6 +145,7 @@ class UFM01Component : public uart::UARTDevice, public Component {
 #ifdef USE_UFM01_CLEAR_ACCUMULATED_FLOW_ACTION
   uint32_t pending_clear_start_ms_{0};
 #endif
+  int32_t read_index_{0};
 
   OperatingMode operating_mode_{OperatingMode::STARTUP};
   StartupPhase startup_phase_{StartupPhase::WAIT};
@@ -172,7 +170,7 @@ class UFM01Component : public uart::UARTDevice, public Component {
 #endif
 
   uint8_t passive_frame_[PASSIVE_FRAME_MAX_SIZE];
-  FrameReader<FRAME_SIZE, FRAME_START_BYTE_1, FRAME_START_BYTE_2> active_reader_;
+  uint8_t data_[FRAME_SIZE];
 
   friend class testing::TestableUFM01;
 };

esphome/components/wts01/wts01.cpp

@@ -4,38 +4,70 @@
 
 namespace esphome::wts01 {
 
+constexpr uint8_t HEADER_1 = 0x55;
+constexpr uint8_t HEADER_2 = 0x01;
+constexpr uint8_t HEADER_3 = 0x01;
+constexpr uint8_t HEADER_4 = 0x04;
+
 ESPHOME_LOG_TAG(TAG, "wts01");
 
 void WTS01Sensor::loop() {
-  this->read_available([this](uint8_t c) {
-    if (const uint8_t *packet = this->reader_.feed(c)) {
-      this->process_packet_(packet);
-    }
-  });
+  this->read_available([this](uint8_t c) { this->handle_char_(c); });
 }
 
 void WTS01Sensor::dump_config() { LOG_SENSOR("", "WTS01 Sensor", this); }
 
-void WTS01Sensor::process_packet_(const uint8_t *packet) {
+void WTS01Sensor::handle_char_(uint8_t c) {
+  // State machine for processing the header. Reset if something doesn't match.
+  if (this->buffer_pos_ == 0 && c != HEADER_1) {
+    return;
+  }
+
+  if (this->buffer_pos_ == 1 && c != HEADER_2) {
+    this->buffer_pos_ = 0;
+    return;
+  }
+
+  if (this->buffer_pos_ == 2 && c != HEADER_3) {
+    this->buffer_pos_ = 0;
+    return;
+  }
+
+  if (this->buffer_pos_ == 3 && c != HEADER_4) {
+    this->buffer_pos_ = 0;
+    return;
+  }
+
+  // Add byte to buffer
+  this->buffer_[this->buffer_pos_++] = c;
+
+  // Process complete packet
+  if (this->buffer_pos_ >= PACKET_SIZE) {
+    this->process_packet_();
+    this->buffer_pos_ = 0;
+  }
+}
+
+void WTS01Sensor::process_packet_() {
   // Based on Tasmota implementation
   // Format: 55 01 01 04 01 11 16 12 95
   // header            T  Td Ck  - T = Temperature, Td = Temperature decimal, Ck = Checksum
-  const uint8_t calculated_checksum = sum_bytes(packet, PACKET_SIZE - 1);
+  const uint8_t calculated_checksum = sum_bytes(this->buffer_, PACKET_SIZE - 1);
 
-  uint8_t received_checksum = packet[PACKET_SIZE - 1];
+  uint8_t received_checksum = this->buffer_[PACKET_SIZE - 1];
   if (calculated_checksum != received_checksum) {
     ESP_LOGW(TAG, "WTS01 Checksum doesn't match: 0x%02X != 0x%02X", received_checksum, calculated_checksum);
     return;
   }
 
   // Extract temperature value
-  const uint8_t raw = packet[6];
+  const uint8_t raw = this->buffer_[6];
 
   // WTS01 encodes sign in bit 7, magnitude in bits 0-6
   const bool negative = (raw & 0x80) != 0;
   const uint8_t magnitude = raw & 0x7F;
 
-  const float decimal = static_cast<float>(packet[7]) / 100.0f;
+  const float decimal = static_cast<float>(this->buffer_[7]) / 100.0f;
 
   float temperature = static_cast<float>(magnitude) + decimal;
 

esphome/components/wts01/wts01.h

@@ -1,7 +1,6 @@
 #pragma once
 
 #include "esphome/core/component.h"
-#include "esphome/core/frame_reader.h"
 #include "esphome/components/sensor/sensor.h"
 #include "esphome/components/uart/uart.h"
 
@@ -15,9 +14,11 @@ class WTS01Sensor final : public sensor::Sensor, public uart::UARTDevice, public
   void dump_config() override;
 
  protected:
-  void process_packet_(const uint8_t *packet);
+  uint8_t buffer_[PACKET_SIZE];
+  uint8_t buffer_pos_{0};
 
-  FrameReader<PACKET_SIZE, 0x55, 0x01, 0x01, 0x04> reader_;
+  void handle_char_(uint8_t c);
+  void process_packet_();
 };
 
 }  // namespace esphome::wts01

esphome/core/frame_reader.h

@@ -1,67 +0,0 @@
-#pragma once
-
-#include <cstddef>
-#include <cstdint>
-#include <type_traits>
-
-namespace esphome {
-
-/// Collects fixed length binary frames of N bytes that start with the header bytes HEADER...; the binary twin of
-/// LineReader. Bytes before a header are skipped; checksums are left to the caller.
-template<size_t N, uint8_t... HEADER> class FrameReader {
-  using pos_t = std::conditional_t<(N <= 0xFF), uint8_t, uint16_t>;
-  static constexpr size_t HEADER_LEN = sizeof...(HEADER);
-  static_assert(HEADER_LEN >= 1 && HEADER_LEN <= 8, "FrameReader takes 1 to 8 header bytes");  // bounds replay_() depth
-  static_assert(HEADER_LEN < N && N <= 0xFFFF, "FrameReader size out of range");
-
- public:
-  /// Feed one byte; returns the completed frame, header included, valid until the next call, or nullptr.
-  const uint8_t *feed(uint8_t c) {
-    pos_t pos = this->pos_;
-    if (pos < HEADER_LEN && c != header_byte(pos)) {
-      // A later byte of the broken header, or c, may start the real one
-      this->buf_[pos] = c;
-      this->replay_(pos);
-      return nullptr;
-    }
-    this->buf_[pos++] = c;
-    if (pos < N) {
-      this->pos_ = pos;
-      return nullptr;
-    }
-    this->pos_ = 0;
-    return this->buf_;
-  }
-
-  /// Number of bytes of the partial frame; 0 after a frame is returned and while looking for a header.
-  size_t length() const { return this->pos_; }
-
-  /// Forget the partial frame and look for a header from the next byte.
-  void reset() { this->pos_ = 0; }
-
-  /// For a frame the caller rejected (bad checksum): drop its first byte and realign on a header in the rest.
-  /// Call only right after feed() returned that frame; use reset() otherwise.
-  void resync() { this->replay_(N - 1); }
-
- protected:
-  // A fold, not an array, so no header table lands in RAM on ESP8266
-  static constexpr uint8_t header_byte(size_t i) {
-    size_t j = 0;
-    uint8_t r = 0;
-    ((r = (j++ == i) ? HEADER : r), ...);
-    return r;
-  }
-
-  // Start over and feed buf_[1..last] again; never completes a frame as last < N
-  void replay_(size_t last) {
-    this->pos_ = 0;
-    for (size_t i = 1; i <= last; i++) {
-      this->feed(this->buf_[i]);
-    }
-  }
-
-  uint8_t buf_[N];
-  pos_t pos_{0};
-};
-
-}  // namespace esphome

tests/component_tests/mipi_spi/test_init.py

@@ -93,6 +93,16 @@ def run_schema_validation(config: ConfigType) -> None:
             r"value must be a power of two for dictionary value @ data\['draw_rounding'\]",
             id="invalid_draw_rounding",
         ),
+        pytest.param(
+            {
+                "model": "custom",
+                "dc_pin": 18,
+                "dimensions": {"width": 320, "height": 240},
+                "init_sequence": [[0xE0] + [0x00] * 129],
+            },
+            r"at most 128 data bytes",
+            id="init_command_too_long",
+        ),
     ],
 )
 def test_basic_configuration_errors(
@@ -606,3 +616,19 @@ def test_identical_init_sequences_share_one_table(
     assert first is not None and second is not None
     assert first.group(1) == second.group(1)
     assert main_cpp.count("mipi_spi_init_sequence[] PROGMEM") == 1
+
+
+def test_init_command_at_buffer_limit(set_core_config: SetCoreConfigCallable) -> None:
+    """A command with exactly 128 data bytes fits the C++ copy buffer."""
+    set_core_config(
+        PlatformFramework.ESP32_IDF,
+        platform_data={KEY_BOARD: "esp32dev", KEY_VARIANT: VARIANT_ESP32},
+    )
+    run_schema_validation(
+        {
+            "model": "custom",
+            "dc_pin": 18,
+            "dimensions": {"width": 320, "height": 240},
+            "init_sequence": [[0xE0] + [0x00] * 128],
+        }
+    )

tests/components/core/frame_reader_test.cpp

@@ -1,143 +0,0 @@
-#include <gtest/gtest.h>
-#include <vector>
-#include "esphome/core/frame_reader.h"
-
-namespace esphome::core::testing {
-
-using Bytes = std::vector<uint8_t>;
-using Frames = std::vector<Bytes>;
-
-// Feeds bytes and collects every completed frame.
-template<size_t N, uint8_t... H> static Frames feed_all(FrameReader<N, H...> &reader, const Bytes &input) {
-  Frames frames;
-  for (uint8_t c : input) {
-    const uint8_t *frame = reader.feed(c);
-    if (frame != nullptr) {
-      EXPECT_EQ(reader.length(), 0u);
-      frames.emplace_back(frame, frame + N);
-    }
-  }
-  return frames;
-}
-
-static_assert(sizeof(FrameReader<4, 0xFF>) == 5);
-static_assert(sizeof(FrameReader<9, 0x55, 0x01, 0x01, 0x04>) == 10);
-static_assert(sizeof(FrameReader<0xFF, 0xAA>) == 0x100);
-static_assert(sizeof(FrameReader<0x100, 0xAA>) == 0x102);
-
-TEST(FrameReaderTest, SingleByteHeader) {
-  FrameReader<4, 0xFF> reader;
-  EXPECT_EQ(feed_all(reader, {0xFF, 0x01, 0x02, 0x02, 0xFF, 0x03, 0x04, 0x06}),
-            (Frames{{0xFF, 0x01, 0x02, 0x02}, {0xFF, 0x03, 0x04, 0x06}}));
-}
-
-TEST(FrameReaderTest, SkipsBytesBeforeHeader) {
-  FrameReader<3, 0xFF> reader;
-  EXPECT_EQ(feed_all(reader, {0x01, 0x02, 0xFF, 0x10, 0x20}), (Frames{{0xFF, 0x10, 0x20}}));
-}
-
-TEST(FrameReaderTest, HeaderByteInsidePayloadIsData) {
-  FrameReader<4, 0xFF> reader;
-  EXPECT_EQ(feed_all(reader, {0xFF, 0xFF, 0xFF, 0x00}), (Frames{{0xFF, 0xFF, 0xFF, 0x00}}));
-}
-
-TEST(FrameReaderTest, LengthTracksPartialFrame) {
-  FrameReader<4, 0xAA, 0xBB> reader;
-  EXPECT_EQ(reader.length(), 0u);
-  reader.feed(0x00);
-  EXPECT_EQ(reader.length(), 0u);
-  reader.feed(0xAA);
-  EXPECT_EQ(reader.length(), 1u);
-  reader.feed(0xBB);
-  reader.feed(0x01);
-  EXPECT_EQ(reader.length(), 3u);
-  reader.reset();
-  EXPECT_EQ(reader.length(), 0u);
-  EXPECT_EQ(feed_all(reader, {0x02, 0xAA, 0xBB, 0x03, 0x04}), (Frames{{0xAA, 0xBB, 0x03, 0x04}}));
-}
-
-TEST(FrameReaderTest, MultiByteHeaderMismatchRestarts) {
-  FrameReader<6, 0x55, 0x01, 0x01, 0x04> reader;
-  EXPECT_EQ(feed_all(reader, {0x55, 0x01, 0x02, 0x55, 0x01, 0x01, 0x04, 0x11, 0x22}),
-            (Frames{{0x55, 0x01, 0x01, 0x04, 0x11, 0x22}}));
-}
-
-TEST(FrameReaderTest, MismatchedByteCanStartHeader) {
-  FrameReader<6, 0x55, 0x01, 0x01, 0x04> reader;
-  // The second 0x55 breaks the first header and starts the real one
-  EXPECT_EQ(feed_all(reader, {0x55, 0x01, 0x55, 0x01, 0x01, 0x04, 0x11, 0x22}),
-            (Frames{{0x55, 0x01, 0x01, 0x04, 0x11, 0x22}}));
-}
-
-TEST(FrameReaderTest, RepeatedHeaderPrefixIsKept) {
-  // AA AA AA BB: the mismatch at the third byte still leaves AA AA matched
-  FrameReader<4, 0xAA, 0xAA, 0xBB> reader;
-  EXPECT_EQ(feed_all(reader, {0xAA, 0xAA, 0xAA, 0xBB, 0x01}), (Frames{{0xAA, 0xAA, 0xBB, 0x01}}));
-}
-
-TEST(FrameReaderTest, OverlappingHeaderPrefix) {
-  // A1 B2 A1 B2: the mismatch on the last B2 keeps the trailing A1 B2 as the start of the header
-  FrameReader<5, 0xA1, 0xB2, 0xA1, 0xC3> reader;
-  EXPECT_EQ(feed_all(reader, {0xA1, 0xB2, 0xA1, 0xB2, 0xA1, 0xC3, 0x07}), (Frames{{0xA1, 0xB2, 0xA1, 0xC3, 0x07}}));
-}
-
-TEST(FrameReaderTest, ResyncFindsHeaderInRejectedFrame) {
-  FrameReader<4, 0xFF> reader;
-  // Started mid-frame: the 0xFF taken as a header was payload; the real frame starts at the second 0xFF
-  const uint8_t *frame = nullptr;
-  for (uint8_t c : {0xFF, 0x12, 0xFF, 0x01}) {
-    frame = reader.feed(c);
-  }
-  ASSERT_NE(frame, nullptr);
-  reader.resync();
-  EXPECT_EQ(reader.length(), 2u);
-  EXPECT_EQ(feed_all(reader, {0x02, 0x02}), (Frames{{0xFF, 0x01, 0x02, 0x02}}));
-}
-
-TEST(FrameReaderTest, ResyncWithoutHeaderStartsOver) {
-  FrameReader<4, 0xFF> reader;
-  const uint8_t *frame = nullptr;
-  for (uint8_t c : {0xFF, 0x01, 0x02, 0x03}) {
-    frame = reader.feed(c);
-  }
-  ASSERT_NE(frame, nullptr);
-  reader.resync();
-  EXPECT_EQ(reader.length(), 0u);
-}
-
-TEST(FrameReaderTest, ResyncKeepsPartialHeaderAtEnd) {
-  FrameReader<5, 0x3C, 0x32> reader;
-  const uint8_t *frame = nullptr;
-  for (uint8_t c : {0x3C, 0x32, 0x00, 0x00, 0x3C}) {
-    frame = reader.feed(c);
-  }
-  ASSERT_NE(frame, nullptr);
-  reader.resync();
-  EXPECT_EQ(reader.length(), 1u);
-  EXPECT_EQ(feed_all(reader, {0x32, 0x01, 0x02, 0x03}), (Frames{{0x3C, 0x32, 0x01, 0x02, 0x03}}));
-}
-
-TEST(FrameReaderTest, ResyncMultiByteHeader) {
-  FrameReader<6, 0x3C, 0x32> reader;
-  const uint8_t *frame = nullptr;
-  for (uint8_t c : {0x3C, 0x32, 0x3C, 0x3C, 0x32, 0x09}) {
-    frame = reader.feed(c);
-  }
-  ASSERT_NE(frame, nullptr);
-  reader.resync();
-  EXPECT_EQ(reader.length(), 3u);
-  EXPECT_EQ(feed_all(reader, {0x0A, 0x0B, 0x0C}), (Frames{{0x3C, 0x32, 0x09, 0x0A, 0x0B, 0x0C}}));
-}
-
-TEST(FrameReaderTest, SixteenBitIndex) {
-  FrameReader<300, 0xAA, 0x55> reader;
-  Bytes input{0x00, 0xAA, 0x55};
-  input.resize(input.size() + 298, 0x42);
-  Frames frames = feed_all(reader, input);
-  ASSERT_EQ(frames.size(), 1u);
-  EXPECT_EQ(frames[0][0], 0xAA);
-  EXPECT_EQ(frames[0][1], 0x55);
-  EXPECT_EQ(frames[0][299], 0x42);
-}
-
-}  // namespace esphome::core::testing

tests/components/display/test_init_sequence.cpp

@@ -0,0 +1,82 @@
+#include <gtest/gtest.h>
+
+#include <cstdint>
+
+#include "esphome/components/display/init_sequence.h"
+
+namespace esphome::display::testing {
+
+TEST(InitSequenceReader, WalksCommandsAndDelays) {
+  static const uint8_t SEQ[] = {0x11, 0x00, 120, 0xFF, 0x3A, 0x01, 0x55, 0x2A, 0x02, 0x00, 0xEF};
+  InitSequenceReader reader(SEQ, sizeof(SEQ));
+  InitSequenceEntry entry{};
+
+  ASSERT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_COMMAND);
+  EXPECT_EQ(entry.value, 0x11);
+  EXPECT_EQ(entry.count, 0);
+
+  ASSERT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_DELAY);
+  EXPECT_EQ(entry.value, 120);
+
+  ASSERT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_COMMAND);
+  EXPECT_EQ(entry.value, 0x3A);
+  ASSERT_EQ(entry.count, 1);
+  EXPECT_EQ(entry.args, &SEQ[6]);
+
+  ASSERT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_COMMAND);
+  EXPECT_EQ(entry.value, 0x2A);
+  ASSERT_EQ(entry.count, 2);
+  EXPECT_EQ(entry.args[0], 0x00);
+  EXPECT_EQ(entry.args[1], 0xEF);
+
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_END);
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_END);
+}
+
+TEST(InitSequenceReader, EmptySequenceEnds) {
+  InitSequenceReader reader(nullptr, 0);
+  InitSequenceEntry entry{};
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_END);
+}
+
+// A count above 127 is a real length, not a flag bit.
+TEST(InitSequenceReader, HonoursFullCount) {
+  uint8_t seq[2 + 253 + 2] = {0x32, 253};
+  seq[2 + 253] = 0x29;
+  InitSequenceReader reader(seq, sizeof(seq));
+  InitSequenceEntry entry{};
+
+  ASSERT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_COMMAND);
+  EXPECT_EQ(entry.value, 0x32);
+  EXPECT_EQ(entry.count, 253);
+  ASSERT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_COMMAND);
+  EXPECT_EQ(entry.value, 0x29);
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_END);
+}
+
+TEST(InitSequenceReader, TruncatedHeaderIsMalformed) {
+  static const uint8_t SEQ[] = {0x11, 0x00, 0x29};
+  InitSequenceReader reader(SEQ, sizeof(SEQ));
+  InitSequenceEntry entry{};
+  ASSERT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_COMMAND);
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_MALFORMED);
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_END);
+}
+
+TEST(InitSequenceReader, ShortArgsAreMalformed) {
+  static const uint8_t SEQ[] = {0x2A, 0x04, 0x00, 0x00, 0x00};
+  InitSequenceReader reader(SEQ, sizeof(SEQ));
+  InitSequenceEntry entry{};
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_MALFORMED);
+  EXPECT_EQ(reader.next(entry), INIT_SEQUENCE_STEP_END);
+}
+
+TEST(InitSequenceReader, CountOverMaxIsMalformed) {
+  static const uint8_t SEQ[] = {10, 0xFF, 0x2A, 0x02, 0x00, 0xEF};
+  InitSequenceReader reader(SEQ, sizeof(SEQ));
+  InitSequenceEntry entry{};
+  ASSERT_EQ(reader.next(entry, 1), INIT_SEQUENCE_STEP_DELAY);
+  EXPECT_EQ(reader.next(entry, 1), INIT_SEQUENCE_STEP_MALFORMED);
+}
+
+}  // namespace esphome::display::testing

tests/components/ufm01/common.h

@@ -20,6 +20,8 @@
 
 namespace esphome::ufm01::testing {
 
+static constexpr uint8_t FRAME_START_BYTE_1 = 0x3C;
+static constexpr uint8_t FRAME_START_BYTE_2 = 0x32;
 static constexpr uint8_t PASSIVE_START_BYTE_2 = 0x64;
 static constexpr uint8_t PASSIVE_START_BYTE_2_WITH_ID = 0x96;
 static constexpr uint8_t FRAME_STOP_BYTE = 0x16;
@@ -129,7 +131,7 @@ class TestableUFM01 : public UFM01Component {
 
   StartupPhase startup_phase() const { return this->startup_phase_; }
 
-  int32_t read_index() const { return this->active_reader_.length(); }
+  int32_t read_index() const { return this->read_index_; }
 
   uint8_t passive_index() const { return this->passive_index_; }
 
@@ -163,7 +165,7 @@ class TestableUFM01 : public UFM01Component {
     this->operating_mode_ = OperatingMode::ACTIVE_STREAM;
     this->last_valid_frame_ms_ = now();
     this->passive_read_pending_ = false;
-    this->active_reader_.reset();
+    this->read_index_ = 0;
   }
 
   void begin_active_wait_frame() {
@@ -180,7 +182,7 @@ class TestableUFM01 : public UFM01Component {
   }
 
   void reset_state() {
-    this->active_reader_.reset();
+    this->read_index_ = 0;
     this->last_valid_frame_ms_ = 0;
     this->passive_index_ = 0;
     this->passive_read_pending_ = false;

tests/components/ufm01/ufm01_frame_test.cpp

@@ -30,15 +30,6 @@ TEST_F(UFM01Test, InvalidActiveFrameChecksumRejected) {
   EXPECT_EQ(this->ufm01_.last_valid_frame_ms(), 0u);
 }
 
-TEST_F(UFM01Test, RejectedActiveFrameResyncsOnStartBytesInside) {
-  // A cut off frame start makes the first 32 bytes invalid; the real frame starts inside them
-  this->mock_uart_.enqueue({FRAME_START_BYTE_1, FRAME_START_BYTE_2, 0x00, 0x00});
-  this->mock_uart_.enqueue(make_active_frame());
-
-  EXPECT_TRUE(this->ufm01_.process_active_stream());
-  EXPECT_EQ(this->ufm01_.read_index(), 0);
-}
-
 TEST_F(UFM01Test, ValidPassiveFrameReadSuccess) {
   auto frame = make_passive_frame();
   this->mock_uart_.enqueue(frame);

tests/unit_tests/components/test_display.py

@@ -1,4 +1,4 @@
-"""Tests for display.add_writer."""
+"""Tests for display.add_writer and display.config_has_writer."""
 
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -6,7 +6,8 @@ import pytest
 
 from esphome import codegen as cg
 from esphome.components import display
-from esphome.const import CONF_LAMBDA
+from esphome.components.display import CONF_SHOW_TEST_CARD
+from esphome.const import CONF_AUTO_CLEAR_ENABLED, CONF_LAMBDA, CONF_PAGES
 
 
 @pytest.mark.parametrize(
@@ -39,3 +40,20 @@ async def test_add_writer_without_lambda_does_nothing() -> None:
 
     process.assert_not_awaited()
     add.assert_not_called()
+
+
+@pytest.mark.parametrize(
+    ("config", "expected"),
+    [
+        ({}, False),
+        ({CONF_AUTO_CLEAR_ENABLED: True}, True),
+        ({CONF_AUTO_CLEAR_ENABLED: False}, False),
+        ({CONF_AUTO_CLEAR_ENABLED: "unspecified"}, False),
+        ({CONF_PAGES: []}, True),
+        ({CONF_LAMBDA: "x"}, True),
+        ({CONF_SHOW_TEST_CARD: True}, True),
+        ({CONF_SHOW_TEST_CARD: False}, False),
+    ],
+)
+def test_config_has_writer(config: dict, expected: bool) -> None:
+    assert display.config_has_writer(config) is expected