Problem with SPI on Pico

[mariusGundersen]

I've found a weird issue with the SPI on the Pico (might be others too, but that's where I'm testing it). My setup is a pic together with the Adafruit eInk Feather Friend, so that I can read images from an SD card and show them on an E-ink display. This means using the SPI to read from the SD card using one chip-select pin and then writing to the e-ink display using another chip-select. I have tested and gotten both the reading from SD card and updating the e-ink display to work, but not together. The error I get is this:

Uncaught InternalError: Timeout on SPI RX

I've searched the code for the string "SPI RX" and found only one potential place it can happen:

Espruino/targets/stm32/jshardware.c

Line 2470 in e6b2fd2

WAIT_UNTIL(jshSPIBufHead[n]!=jshSPIBufTail[n], "SPI RX");

This happens when I try to read from the SD card after writing to the e-ink display. I'm using the chip-select to toggle which device I want to communicate with, but something still seems to go wrong. After a lot of trial and error and experimenting I found a workaround: changing from spi.write(data, cs) to spi.send(data, cs) when communicating with the e-ink display. The display has no MISO pin, so I've been using write() since there is no data coming back. But it seems like this is messing with the internal SPI state machine. The code for recreating this is fairly simple:

SPI1.setup({
    sck: B3,
    miso: B4,
    mosi: B5,
});

E.connectSDCard(SPI1, A5);
require("fs").readdirSync(''); // this works, returns a list of files

// write to SPI1 but using another chip select pin
SPI1.write(0x10, A6)

require("fs").readdirSync(''); // now it fails

// setting up the SPI and SD card again fixes the problem
SPI1.setup({
    sck: B3,
    miso: B4,
    mosi: B5,
});

E.connectSDCard(SPI1, A5);
require("fs").readdirSync(''); // this works, returns a list of files

It seems like the write code is messing up the read code, but I'm unable to debug any deeper than this.

[gfwilliams]

Thanks! That's really helpful to track this down - just to check, you're on the latest 2v25 firmware? And did you check on other firmwares? (it doesn't matter if not).

[mariusGundersen]

I'm fairly sure I'm on the latest, yes. I haven't tried another version

[gfwilliams]

I've been able to reproduce without actually setting up an SD card on the Pico, but I'm pretty sure I found the issue.

I've put a fix in, so I think if you try a cutting edge build now it should be fixed?

[mariusGundersen]

yes, works great with the latest build, thanks!