Apps: Inline CMSIS-DAP code, fix and test serial issues#110
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The partial flashing code already duplicated significant portions of the dapjs protocol stack. Consolidate everything into a single cmsis-dap.ts module covering the subset we use: SWD transport, Cortex-M debug, and DAPLink serial/flash vendor commands. Also renames DAPWrapper to USBDeviceWrapper and disambiguates device field names (bleDevice/usbDevice).
Fix stale serial data appearing after flash by addressing a race in the serial stop/start cycle. When stopSerial() is called, an in-flight serialRead() can still deliver data after the stop, refilling any consumer line buffer that was cleared on reset. Fix by suppressing data delivery once polling is set to false, and by firing the serialreset event after the polling loop actually exits rather than when stop is requested. Drain DAPLink's serial buffer before flash to discard output that accumulated between the last serial read and the halt. After flash, start serial listening before resetting (partial flash only) so early program output is captured in DAPLink's 512-byte ring buffer. Simplify flashAsync: remove the disconnect/reconnect cycle (invalidate DAP state instead, keeping USB open) and remove the timeout-based fallback from partial to full flash which masked connection problems. Minor: - Strip \r in demo app serial listener (for CRLF) - Fix vitest exclude pattern for build directory
Rename reconnectDaplink for clarity. Add ability to inject faults into flashing via the demo app to test this flow.
Move board info caching and logging up to connection.ts, reducing device-wrapper.ts to a thin composition root. Rename fields for clarity: device→usbDevice/bleDevice for raw devices, connection→device for wrapper state.
We now control all sources of errors other than the browser cases matched by regexp. Review the browser ones and link to the Chromium source, which fortunately proves they're not localized.
DAPLink's CDC serial path races with WebUSB vendor serial reads for the same UART ring buffer, causing truncated serial output after flash. Work around this by pushing NUL bytes through the target's UART to fill DAPLink's internal buffers before flashing. Once full, CDC stops consuming and post-flash output is preserved for vendor reads. V1 (nRF51) runs a Thumb blob for the legacy byte-at-a-time UART. V2 (nRF52833) uses SWD register writes to trigger a UARTE DMA transfer. Both paths fully configure the UART from scratch (pins, baud rate) since the previous program may not have set it up. Only applied on the first flash after physical USB connection and only when serial listeners are attached. See: ARMmbed/DAPLink#903
Tests basic flashing flows including checking serial output. Move the hex files as they're useful more widely than the capacitor project. Remove fault injection from the demo now hardware-test has it.
microbit-matt-hillsdon
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Apr 29, 2026
This contains the pre-1.0 breaking API changes and USB serial re-work. We'll run this on Python beta for a bit to build confidence as the BLE code has had far more real use than the USB changes. This should improve serial issues after first physical connection + flash and extra serial from previous programs leaking into subsequent ones. Relevant fixes: - Workaround for the bad response issue - microbit-foundation/microbit-connection#72 - Use DAPLink vendor command for serial number - microbit-foundation/microbit-connection#103 - Inline CMSIS-DAP code, fix and test serial issues - microbit-foundation/microbit-connection#110 - Fix UICR not updated during WebUSB partial flashing - microbit-foundation/microbit-connection#113
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This targets the apps branch because of the scale of the change and the fact it's targeting 1.0 release rather than because of the apps as such.