203 lines
7.8 KiB
Markdown
203 lines
7.8 KiB
Markdown
# 11 — Blockers A + B resolved + frontend integration
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Follow-up to `10_phase3_webcam_test.md`. Documents the three fixes
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that took `esp_camera_init()` from "always fails" to "PASSES under
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QEMU", plus the frontend pieces that ship the experience to end users.
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## Blocker A — I²C NACK timing (RESOLVED)
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### Diagnosis
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The picsimlab fork's I²C bus has a catch-all slave (`picsimlab_i2c`
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type) registered alongside real slaves. Its `match_and_add` callback
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**always returns true** so it forwards every transaction to the
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worker process for inspection. When the worker doesn't recognise the
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address, the original `_on_i2c_event` returned `0` (= ACK in QEMU's
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`I2CSlaveClass.event` convention), making the controller report
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"slave acked" for **every** address scanned by `SCCB_Probe`.
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The upstream `esp_camera.c` walks `camera_sensor[]` in order:
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```
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[0] OV7725 → 0x21
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[1] OV2640 → 0x30
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…
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```
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`SCCB_Probe(0x21)` returned ESP_OK (false positive), so the driver
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ran the OV7725 chip-id checks, failed, then ran the next sensor at
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0x21 (OV7670, GC0308, GC032A — they share the address), failed all
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of them, and **never advanced to OV2640 at 0x30**.
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### Fix
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Two-line change in
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`backend/app/services/esp32_worker.py:_on_i2c_event`: when there is
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no slave for the address AND the event is `START_SEND` /
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`START_RECV`, return non-zero. That signals NACK to the bus core,
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which sets `ACK_ERR` in the controller's `int_raw_reg`, which
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propagates back through `i2c_master_cmd_begin` as `ESP_FAIL`, which
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makes `SCCB_Probe` return `ESP_FAIL`, which makes the
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`camera_sensor[]` loop `continue` to the next entry.
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```python
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if op in (0x00, 0x01) and resp == 0 and addr not in _i2c_responses:
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return 1
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```
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A secondary fix in
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`third-party/qemu-lcgamboa/hw/i2c/picsimlab_i2c.c:picsimlab_i2c_match`
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declines to claim addresses when no host-side I²C event handler is
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registered (defensive — protects builds where the worker hasn't
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loaded yet).
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### Verification
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The I²C trace now shows ONE probe at 0x21 (NACK) and the driver
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silently advances to 0x30. The OV2640 SCCB device responds with the
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correct chip-id (`PID=0x26 VER=0x42 MIDH=0xa2 MIDL=0x7f`), the
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upstream driver runs `OV2640_JPEG_INIT` register sequence, and
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`esp_camera_init` returns **`ESP_OK`** for the first time:
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```
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velxio-esp32-cam-demo boot
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camera_init ok
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```
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## Blocker B — Continuous EOFs (RESOLVED)
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### Diagnosis
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Real OV2640 produces pixels at PCLK rate while VSYNC is low, with the
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ESP32 firmware's I²S+DMA peripheral autonomously walking a
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ring of `lldesc_t` descriptors and firing `in_suc_eof` after each
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descriptor's worth of samples. The `cam_hal.c` framectrl FreeRTOS
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task reads these events from a queue and accumulates frames.
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My initial `esp32_i2s_cam.c` fired EOF **once per `rx_start` 0→1
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edge**. After the first frame, the framectrl task waited forever for
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the second EOF that never came. `fb_get` blocked.
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### Fix
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Two changes in `hw/misc/esp32_i2s_cam.c`:
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1. **`QEMUTimer *eof_timer`** scheduled every 16 ms (60 fps cadence)
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while `rx_start = 1`. On each tick, walk one chunk's worth of
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samples and fire EOF.
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2. **Ring-aware walker**: the new `walk_dma_chain` scans the
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linked-list looking for the first descriptor with `owner=1`,
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fills it, and stops. Rotation through the ring happens naturally
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because the driver gives back the previous descriptor (sets
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`owner=1`) by the time the next tick fires.
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The timer is started by `maybe_arm_capture()` (rx_start edge) and
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stopped by `cancel_eof()` (rx_start drop edge or device reset).
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### Side fix — JPEG EOI padding
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`cam_hal.c` validates each captured frame by scanning backwards from
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the buffer end for the JPEG EOI marker `0xFF 0xD9`. With short JPEGs
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(typical ~10 KB) padded into a 32 KB DMA buffer, the validator
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finds `0xAA` (the original idle pattern) and rejects the frame.
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`next_pixel_byte` now alternates `0xFF 0xD9 0xFF 0xD9 …` once the
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real JPEG is exhausted. The validator finds an EOI near the buffer
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end and accepts the frame. (Real OV2640 produces variable-length
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JPEGs and the driver handles the pad bytes via the `length` field on
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the descriptor; we approximate that behaviour without modelling
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VSYNC timing precisely.)
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## Phase D status — `esp_camera_fb_get` (PARTIAL)
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### What works
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- `esp_camera_init()` succeeds end-to-end ✓
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- Driver runs full OV2640 init register sequence ✓
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- I²S DMA fires repeatedly at ~60 fps under emulation ✓
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- Frames pushed via `velxio_push_camera_frame()` reach firmware
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memory in the correct `dma_elem_t` packed format ✓ (verified by
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`test_frame_roundtrip_live`)
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### What still doesn't work
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`esp_camera_fb_get()` returns NULL even when frames are pushed. The
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upstream `cam_hal.c::cam_take` does internal validation beyond the
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EOI scan (checks frame size against descriptor `length` totals,
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verifies the SOI marker at the start, runs `ll_cam_dma_filter_jpeg`
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to unpack `dma_elem_t` → plain bytes). One of these checks is
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failing silently.
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### Workaround in place
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The Phase 1+2+3a path through `frame_roundtrip.ino` (which programs
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I²S directly without going through cam_hal) fully works and is
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covered by passing tests. User sketches that need raw frames TODAY
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can copy the `frame_roundtrip.ino` pattern.
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### Path forward
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Inspect `cam_hal.c::cam_take` with a debug-instrumented build to find
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which check rejects the frame. Likely candidates (in order of
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probability):
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1. `ll_cam_dma_filter_jpeg` produces zero output because the filter
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reads the descriptor's `length` field and expects bytes-real-bytes
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not bytes-stored. My walker sets `length = will_fill_samples * 4`
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(stored bytes). Should probably be `length = will_fill_samples * 2`
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(real bytes).
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2. The frame's accumulated size across descriptors doesn't match
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what `cam_obj->fb->len` expects. (fb_count=1 mode has a
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simpler path but more rigid size assumptions.)
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3. `cam_verify_jpeg_eoi` runs on the **unpacked** buffer (post-filter)
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and rejects frames that don't terminate cleanly.
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Each is a 1–3 hour debugging session with `qemu_log_mask` instrumentation
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on the QEMU side and `ESP_LOG_DEBUG` enabled on the firmware side.
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## Frontend integration shipped
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End-users now have a one-click flow:
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```
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frontend/src/hooks/useWebcamFrames.ts ← getUserMedia + capture loop
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frontend/src/components/simulator/CameraToggle.tsx ← canvas-header button
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frontend/src/components/simulator/SimulatorCanvas.tsx ← renders the button for esp32-cam
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frontend/src/simulation/Esp32Bridge.ts ← sendCameraAttach/Frame/Detach
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```
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Click "Camera" → browser asks permission → 320×240 JPEG frames at
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10 fps stream over the existing simulator WebSocket → backend
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forwards to worker → worker calls `velxio_push_camera_frame` →
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QEMU device delivers bytes to the firmware. **The full chain is
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live as soon as the upstream `fb_get` blocker (Phase D follow-up
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above) is resolved.**
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For now, the chain is verified by `test_frame_roundtrip_live` (uses
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the same `Esp32Bridge.sendCameraFrame` path under test).
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## User-facing demo sketch
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`sketches/webcam_demo/webcam_demo.ino` ships as a starter. Once
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loaded:
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```cpp
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camera_config_t cfg = { /* AI-Thinker pinout */ };
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cfg.fb_location = CAMERA_FB_IN_DRAM; // VELXIO note
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esp_camera_init(&cfg); // works under emulation
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camera_fb_t* fb = esp_camera_fb_get();
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Serial.printf("frame %u bytes\n", fb->len);
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esp_camera_fb_return(fb);
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```
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The sketch documents the `fb_location` quirk inline so users don't
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hit the same heap allocation failure I hit during debugging.
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## Sources
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Same as `10_phase3_webcam_test.md` plus:
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- [QEMU I²C bus core — i2c_do_start_transfer](https://github.com/qemu/qemu/blob/master/hw/i2c/core.c) — match-and-NACK semantics
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- [ESP-IDF i2c_master_cmd_begin source](https://github.com/espressif/esp-idf/blob/release/v4.4/components/driver/i2c.c) — how ACK_ERR propagates
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- [esp32-camera/driver/cam_hal.c — frame validation](https://github.com/espressif/esp32-camera/blob/master/driver/cam_hal.c)
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