Reject unsupported color schemes at direct-write START#3
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nRF firmware only renders BW (color_scheme 0) and BWR (color_scheme 1).
map_panel_ic_to_model_id() maps every nonzero color_scheme to a BWR model
and direct-write START sizes the transfer with a single BWR plane byte
count. For BWY, 2bpp and 4-gray schemes the client streams a differently
sized payload, so the firmware over/under-runs RAM and refreshes garbage
while still ACKing success.
Check display_config->color_scheme at direct-write START and reject any
scheme other than 0/1 with the standard 4-byte NACK frame
{0xFF, cmd, RESP_ERR_UNSUPPORTED_SCHEME, 0x00} before powering the panel.
The client's validate_ack_response() sees 0xFF70 instead of the 0x0070
ACK echo and raises InvalidResponseError, so it fails fast instead of
rendering garbage. BW and BWR are unchanged.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012g2e8mr132vcizx92WsgiR
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Problem
map_panel_ic_to_model_id()(EPD/EPD_driver.c:325) maps any nonzerocolor_schemeto a BWR model, andhandle_direct_write_start()sizes the transfer using a single BWR plane byte count (row_bytes * height). The nRF firmware genuinely renders only two schemes: BW (0) and BWR (1). For BWY (2), 2bpp (3/5) and 4-gray (4/6), the client streams a payload of a different size than the firmware computes, so it over/under-runs display RAM and refreshes garbage — while still ACKing success to the client.Fix
At direct-write START, check the display's configured
color_scheme. If it is anything other than 0 (BW) or 1 (BWR), reply with the standard 4-byte NACK frame{0xFF, cmd, RESP_ERR_UNSUPPORTED_SCHEME, 0x00}and return before powering the panel or streaming. The unsupported color schemes are not implemented; they are cleanly rejected.Accepted vs rejected schemes
0(BW),1(BWR) — behavior unchanged.2(BWY),3/5(2bpp),4/6(4-gray), and any other value; also a NULLdisplay_config.Error frame
{0xFF, 0x70, 0x02, 0x00}—0x70is the low byte ofCMD_DIRECT_WRITE_START,0x02is the newRESP_ERR_UNSUPPORTED_SCHEMEcode. This matches the existing 4-byte NACK convention already used for config errors.Client recognition
The START ACK is
{0x00, 0x70}→ command code0x0070, which the client'svalidate_ack_response()accepts. The NACK's first two bytes are0xFF70, which is not in the valid ACK set{0x0070, 0x8070}, sovalidate_ack_response()raisesInvalidResponseError(protocol/responses.py). The client fails fast — it does not hang or proceed to stream.Testing
arm-none-eabi-gccand the nRF SDK build environment are not available here, so a full firmware build was not run. The changed logic was extracted into an isolated translation unit and compiled clean withgcc -std=c11 -Wall -Wextra -Werror(including the logging-disabled path). Change is surgical: BW and BWR paths are untouched.🤖 Generated with Claude Code
https://claude.ai/code/session_012g2e8mr132vcizx92WsgiR