Flickering SPI_Buttons

[dracc]

Hi!
I'm trying to use an RP2040 Zero as an SPI Button bridge.
Rough schematic as follows:

The module called "RP2040_3" reports correct button presses over USB, but as a debugging measure I've replaced the actual buttons with a simple counter. The counter waits for 250 ms and then adds 1 to the "buttons array", a simple volatile uint32_t.
On the second core, I've set up SPI to send the buttons array as often as possible.

The RP2040 is running at 84 MHz and spi0 reports a baudrate of 1312500 Hz which should match the OpenFFBoard "medium" SPI speed preset (42 000 000 / 32).
So far so good. With gamepadtester.com, I can see that the first byte is received as expected and counting upwards. But all other bytes (I'm targetting 16 buttons but have 32 enabled) seem to be set to one. All buttons/bits (0-31) flicker a few times (~20?) per second when set to one.

What am I missing?

[dracc]

I had missed the SPI dialect in use.
I assumed that 8 bits per transfer, for a total of 4 transfers per button array, would work.
The current firmware wants all the buttons to be transferred at once.

This means I'm currently limited to 16 buttons max, as the RP2040's SPI device can't send more than that at once. Maybe a PIO based SPI device could do better but I'm fine with this for now.