Finding MJ-14 (Silabs side)

The read-config chunk loop in handle_config_read (opendisplay_pipe.c) capped the number of response chunks at a hardcoded max_chunks = 10. Because the cap was a magic number decoupled from MAX_CONFIG_SIZE, any config whose length exceeds the cap's reach can never be fully read: the client loops until it has received total bytes, but the firmware stops sending after the cap, so the client retries/times out indefinitely.

Fix

Derive the cap from MAX_CONFIG_SIZE so a full config is always readable and the cap scales automatically if MAX_CONFIG_SIZE changes:

const uint16_t max_chunks =
    (uint16_t)((MAX_CONFIG_SIZE + (MAX_RESPONSE_DATA_SIZE - 6u) - 1u) /
               (MAX_RESPONSE_DATA_SIZE - 6u));

Chunk 0 carries a 4-byte header plus a 2-byte length prefix (94 payload bytes); later chunks carry only the 4-byte header (96 payload bytes). Sizing against the smallest per-chunk payload (MAX_RESPONSE_DATA_SIZE - 6 = 94) guarantees sufficiency. Per-chunk size and framing are unchanged.

Old vs new max readable size

With MAX_RESPONSE_DATA_SIZE = 100:

• Old: cap = 10 chunks → 94 + 9×96 = 958 B max readable.
• New: cap derived from MAX_CONFIG_SIZE → covers the full config by construction.

Note: on the Silabs side MAX_CONFIG_SIZE is currently 512, which is already below the old 958 B reach, so the MJ-14 symptom does not manifest here today — this change is hardening that ties the read cap to MAX_CONFIG_SIZE and removes the fragile magic number. With MAX_CONFIG_SIZE = 512 the derived cap is 6 chunks (574 B raw capacity), still covering the full config. MJ-14 also requires the companion read-cap raises on the nRF and Arduino firmwares, where MAX_CONFIG_SIZE is larger and the bug is live.

Verify

No SLC / arm-none-eabi-gcc / cmake_gcc toolchain available in this environment, so no firmware build. The full file cannot be host-compiled without the Silabs SDK headers (sl_bt_api.h). The isolated cap expression was host-compiled clean under gcc -Wall -Wextra -Wconversion and verified to yield max_chunks = 6 covering 512 B.

🤖 Generated with Claude Code

https://claude.ai/code/session_012g2e8mr132vcizx92WsgiR