SPI timeout in `_send_command` on Inky Impression 7.3"

[bphenriques]

For transparency, I am trying to make a inkypi setup to work and using AI assistant as a I am not familiar with this domain but I am with codomg in general. The report seems sensible (adjusted a bit) and I am using the workaround successfully. I prefer not to open a pull-request unless someone suggests as I am not the best judget to decide if the workaround is the real fix or if there is a better solution.

If I understand we are trying to exceeding the threshold of the channel and we should instead send in chunks.

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Every call to show() fails with TimeoutError: [Errno 110] Connection timed out. The timeout is ~6 seconds regardless of SPI clock speed.

_send_command in inky_e673.py sends the full frame buffer (~384 KB) via a single xfer3() call, which hits the kernel SPI DMA timeout on recent kernels.

_spi_write in the same file already handles this correctly by chunking large transfers into 4 KB xfer calls using _SPI_CHUNK_SIZE, but _send_command doesn't.

Traceback

File ".../inky/inky_e673.py", line 295, in show
    self._update(buf.astype("uint8").tolist())
File ".../inky/inky_e673.py", line 251, in _update
    self._send_command(EL673_DTM1, buf)
File ".../inky/inky_e673.py", line 377, in _send_command
    self._spi_bus.xfer3(data)
TimeoutError: [Errno 110] Connection timed out

Kernel dmesg:

spidev spi0.0: SPI transfer timed out
spi_master spi0: failed to transfer one message from queue

Workaround

Patching _send_command to use chunked xfer calls fixes the issue:

         if data is not None:
             self._gpio.set_value(self.dc_pin, Value.ACTIVE)
-            self._spi_bus.xfer3(data)
+            for x in range(((len(data) - 1) // _SPI_CHUNK_SIZE) + 1):
+                offset = x * _SPI_CHUNK_SIZE
+                self._spi_bus.xfer(data[offset:offset + _SPI_CHUNK_SIZE])

Environment

• Inky Impression 7.3" (Spectra 6)
• Raspberry Pi Zero 2W
• Kernel 6.12.75+rpt-rpi-v8
• inky 2.3.0
• spidev.bufsiz=131072