Red video distortion when access USB filesystem

[astralaster]

Current firmware produce red visual distortions (lines) when the filesystem is accessed via USB. Its currently unknown why exactly this happens.

[zbyti]

when I used a USB2.0 pendrive data was read very slowly, it was very visible.

now I use a USB3.0 pendrive and it is less bothersome, but it occurs, something like using keyboard on the ZX80 :D

[paulscottrobson]

I suspect this is activity on the part of tinyUSB, maybe locking out the other core ? Needs an RP2040 expert as such is way beyond my knowledge of it.

[paulscottrobson]

Also suspect #66 is related to this.

[astralaster]

I did some more testing today. Its now pretty obvious that the problem is flash access. I did remove the PICO_FLASH_SPI_CLKDIV=4 and the boot_stage2 stuff and it does not show the red line glitches at all. We need to reevaluate if its feasible to use PICO default settings for the flash. Otherwise we could try to force specific functions into ram to avoid those flash accesses.

[paulscottrobson]

Don't want to give up RAM to that unless it's a small amount. It's a bit in short supply as it is. I suppose the only real way to try it out is to let people try it and see if it works ?

Also found this raspberrypi/pico-sdk#1304 which suggests setting PICO_XOSC_STARTUP_DELAY_MULTIPLIER as a fix to a similar problem ? I think booting problems were the issue ?