Segment pool entries are 20 bytes on this build, not the nominal 16 that
struct tcp_seg suggests; the comment now quotes the measured figure.
The MEM_SIZE justification did not close as written: two connections at
~6KB each is ~12KB, which fits inside the old 16KB heap. The missing
term is that mem.c is first-fit, so what has to be free is a contiguous
1.5KB block, and at 75% occupancy interleaved with ARP, DHCP/DNS and
mDNS allocations the largest run collapses long before the total does.
That is also why the failure looked intermittent. Spelled out in both
the Python comment and the header template.
Hoist the lwIP sizing values to module constants so the two numeric
invariants can be tested: the segment pool must stay above the per-PCB
send queue, and MEM_SIZE must stay under 64000 or lwIP widens
mem_size_t to u32_t. Both were previously enforced by prose alone, and
the first would silently rebuild the starvation this change removes.
The generated header is byte identical.
J. Nick Koston
ac259c1565