Add DotPad buffered-receive and skipped BLE tests#19942
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SaschaCowley
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@bramd - is this ready for review? |
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Replace the fragile _onReceive that did inline blocking reads with a buffered-receive approach that accumulates bytes and extracts complete packets. This handles resynchronization on bad sync bytes, buffer overflow protection, and partial-packet buffering. Works with both byte-at-a-time delivery (Serial) and packet-based delivery (BLE). Extract _processPacket from the old inline parsing for clarity. Add 9 unit tests covering: complete packet, byte-at-a-time, partial chunks, multiple packets, resync, overflow, incomplete, empty, and partial header. All pass. Add 5 skipped BLE-specific DotPad tests (TDD skeleton for PR C): _isBleDotPad, check(), addBleDevices registration, _tryConnect BLE. Also fixes "Received responce" typo → "Received response".
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Two correctness fixes to the buffered-receive path: - Clear _receiveBuffer at the start of each _tryConnect probe. The buffer is instance-level and was reused across auto-detect probes; the USB match is a generic FTDI VID, so stray bytes from a non-DotPad device on an earlier port could prefix and corrupt the real device's first response. - Validate the declared packet length at parse time instead of capping the accumulation buffer. Real DotPad frames are small, so a declared length beyond DP_MAX_PACKET_SIZE means a false/garbled header: discard one byte and resync. This drops the old pre-extraction buffer wipe, which (a) discarded multi-packet bursts exceeding 512 bytes before processing any of them and (b) could never assemble a frame larger than 512 bytes. It also fixes a stall where a false sync followed by a large bogus length waited indefinitely (recoverable only by wiping queued real packets). Tests: replace test_bufferOverflow_cleared (obsolete semantics) with test_implausibleLength_resynchronize, and assert extracted packet body content in test_completePacketAtOnce to cover the header-stripping slice.
Replace the old "covered by the GNU General Public License / See the file COPYING" reference with the current two-line license reference documented in projectDocs/dev/copyrightHeaders.md, across the files touched in this PR.
Replace "frame" with "packet" in the comments/docstrings touched in this PR to match the terminology used in the code (packet, packetBody, packetLength).
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@seanbudd Yes, this is ready now. |
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Link to issue number:
N/A. This is a follow-up to #19122 (DotPad BLE support) and #19838 (hwIo.ble module). As discussed in those PRs, the work is being split into three smaller PRs. This is "PR B" — the buffered-receive implementation and skipped BLE tests in preparation for the final BLE driver integration in PR C. There is no standalone issue tracking this change.
Summary of the issue:
The DotPad driver's
_onReceivemethod reads remaining packet bytes synchronously viaself._dev.read()and raisesRuntimeErroron any malformed byte, which can kill the display connection. This approach also cannot handle BLE's packet-based delivery model where entire packets arrive in a single callback. The buffered-receive replaces this with a more robust approach as a prerequisite for BLE support.Description of user facing changes:
DotPad braille displays now handle malformed serial data more gracefully. Instead of crashing the display connection on a single corrupted byte, the driver resynchronizes and continues operating. In practice, since DotPad devices currently only connect over USB serial (which is a stable connection), users are unlikely to notice this change. The real benefit comes when BLE support lands in PR C, where packet-based delivery makes the buffered approach essential.
Description of developer facing changes:
_onReceive(self, header1: bytes)with a buffered-receive approach_onReceive(self, data: bytes)that accepts variable-length input (1 byte from Serial, full packets from BLE)._processPacket(self, packetBody: bytes)from the old inline parsing for clarity.DP_MAX_PACKET_SIZEprotocol constant todefs.py.Description of development approach:
Ported the buffered-receive logic from the
dotpad-blebranch (#19122), keeping only the transport-agnostic parts. No BLE-specific code is included — that lands in PR C.The approach replaces synchronous
self._dev.read()calls within the callback with a_receiveBufferthat accumulates bytes across callbacks. Complete packets are extracted from the buffer as they become available.Testing strategy:
Unit tests: 9 unskipped tests covering:
Additionally, 5 skipped BLE-specific tests (
_isBleDotPad,check(),addBleDevicesregistration,_tryConnectBLE path) are included as a TDD skeleton for PR C.rununittests.bat: 1095 tests, 5 skipped, all pass.ruff,pyright,markdownlintall pass.runcheckpot.bat: 0 errors.Manual testing: Tested with a DotPad connected over USB serial. The display works correctly with the new buffered-receive code — navigation, key input, and braille output all function as expected.
Known issues with pull request:
None.
Code Review Checklist:
_onReceive,_processPacket