Reading mipidsi's interface/spi.rs: send_command writes the command byte and its
parameters as TWO separate SpiDevice transactions, so a normal SpiDevice de-asserts
CS between them. The ST7796 needs CS continuous across command+parameters, so
MADCTL/COLMOD/B6 args never loaded → default scan/orientation → 1/4 + rotated
(parameter-less commands and the pixel stream still worked, which is why it lit up).
CircuitPython's FourWire holds CS low for the whole command; replicate that: drive
the real CS (GP5) low for the session and give ExclusiveDevice a no-op CS. DC alone
selects command vs data.
Diagnosed entirely on the host: panelsim (new) decodes mipidsi's actual command/
pixel stream into a PNG and rendered perfectly, proving the protocol was right and
the bug was in the physical SPI/CS layer — then the driver source confirmed it.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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