Roflin
1e370deb49
a2e8e5c batched TXDATA writes into 64-byte chunks and broke ACKs outright --
"no ACK after 20 tries". My regression, and CLAUDE.md warns about exactly
this: tx_bytes is 16 deep and BBARegisterFile silently drops bytes when
w_rdy is low, because SPI cannot back-pressure.
Within a single transaction the bytes arrive back-to-back at EXI speed, far
faster than TXFrameDrain starts consuming, so a 64-byte chunk overran the FIFO,
the frame went out truncated, and no valid ACK ever reached the host.
Byte-by-byte worked only because the per-byte EXI overhead happened to pace
the drain -- which is also why it was slow.
Chunk is now 8, half the FIFO depth: it cannot overflow even if the drain
consumes nothing for the whole transaction, while still cutting a 60-byte ACK
from ~60 transactions to 8. Noted in both the source and CLAUDE.md not to
raise it without deepening tx_bytes or giving the TX path real back-pressure.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>