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[modbus_client] Add read/write multiple registers (FC 0x17) (#18215)

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This commit is contained in:
Bonne Eggleston
2026-08-10 15:18:48 -05:00
committed by GitHub
parent 8a16ead8ce
commit 596827c51c
12 changed files with 520 additions and 52 deletions
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tests/components/modbus/modbus_client_device_test.cpp
+29
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@@ -118,6 +118,35 @@ TEST(ModbusClientDeviceFanOut, ReadHoldingRegistersSuccess) {
EXPECT_FALSE(call.status.has_value());
}
// FC 0x17: the response carries only the read block, so it decodes as a holding-register read of the read
// start/count. The write half has no client-side ack callback - it is confirmed by a successful response.
TEST(ModbusClientDeviceFanOut, ReadWriteMultipleRegistersDeliversReadBlockAsHolding) {
RecordingDevice device;
// read 2 regs at 0x0010, write 1 reg (0x00FF) at 0x0020
const uint8_t request[] = {0x17, 0x00, 0x10, 0x00, 0x02, 0x00, 0x20, 0x00, 0x01, 0x02, 0x00, 0xFF};
const uint8_t response[] = {0x17, 0x04, 0x00, 0x2A, 0x01, 0x00}; // read-back: 0x002A, 0x0100
device.on_response(request, response);
ASSERT_EQ(device.holding_calls.size(), 1u);
const auto &call = device.holding_calls.front();
EXPECT_EQ(call.start_address, 0x0010); // the READ start address, not the write
EXPECT_EQ(call.registers, (std::vector<uint16_t>{0x002A, 0x0100}));
EXPECT_FALSE(call.status.has_value());
EXPECT_TRUE(device.write_multiple_registers_calls.empty()); // no separate write-ack on the client side
}
// A 0x17 response shorter than the requested read count is self-consistent but wrong; it must be diverted
// to on_custom_response(), never clamped and delivered as if complete.
TEST(ModbusClientDeviceFanOut, ReadWriteMultipleRegistersShortResponseGoesToCustom) {
RecordingDevice device;
const uint8_t request[] = {0x17, 0x00, 0x10, 0x00, 0x02, 0x00, 0x20, 0x00, 0x01, 0x02, 0x00, 0xFF};
const uint8_t response[] = {0x17, 0x02, 0x00, 0x2A}; // only 1 register, but 2 were requested
device.on_response(request, response);
EXPECT_TRUE(device.holding_calls.empty());
EXPECT_EQ(device.custom_requests.size(), 1u);
}
TEST(ModbusClientDeviceFanOut, ReadInputRegistersDelegateToGeneric) {
GenericDevice device;
const uint8_t request[] = {0x04, 0x00, 0x10, 0x00, 0x01};