ST7789 PIO driver sending flipped bytes

[sfe-SparkFro]

Using the SPI driver, the first byte sent is 0x01 (reset command), as expected:

Using the PIO driver, the first byte is flipped (LSB instead of MSB order):

Above is with out_shiftdir = rp2.PIO.SHIFT_RIGHT. If it's changed to out_shiftdir = rp2.PIO.SHIFT_LEFT, then no data is output:

According to the example that this driver is based on, it should shift left. Not sure what else needs to be changed to make it output correctly.

[sfe-SparkFro]

Fixed by fc54ace

sm.put(data) writes every byte of data (assuming data has 8-bit element size) into the state machine's 32-bit FIFO. The state machine then shifts 8 bits left (which is leading zeros) before pulling the next 32-bit word from the FIFO and repeating. Fortunately, there's a built-in MicroPython feature to shift the bits over, so the 8 bits we care about get shifted out.