Slowing down flash access when overclocking RP2350

[KevinBDSL]

Hi
I'm using a Pico 2 for a project that uses the PICO-DVI library to generate DVI signals to drive a display.

Part of the ability to do this is down to the ability to overclock the RP2040/2350 chip and run the PIO modules at a higher clock rate.

The PCO-DVI library increases the clock speed depending on the screen resolution required.
For 640x480 to clock is running at 252Mhz
I'd really like to get this to run at 800x600 which requires a 400MHz clock!!. I've successfully achieved 360MHz

My problem is that as soon as the code increases the clock speed my program appears to stop running. My suspicion is that the program is no longer being read from the flash memory.
I would like to try to slow the flash clock down using the SPI /4 option to test this hypothesis but the Boot Stage 2 menu option in Tools is not available on the Pico, Pico2 or Generic RP2530 board types.

Can you point me in the right direction to either enable the Boot Stage 2 menu option for PICO2 or Generic RP2350 or to permanently set the SPI /4 option.

Thanks
Kevin

[earlephilhower]

Can you point me in the right direction to either enable the Boot Stage 2 menu option for PICO2 or Generic RP2350 or to permanently set the SPI /4 option.

The RP2350 ROM no longer has a call out to user code to set up the flash QSPI interface (i.e. no BOOT2 anymore). IIRC they have developed a set of safe configs for the most common flash devices.

I think you will need to manually adjust the QSPI configuration registers. See https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.pdf pages 1240-1241 and M0_TIMING (flash is M0, PSRAM is M1)

That said, you are also trying to overclock from the official 150MHZ to 400MHZ (that would make the Celeron 300A envious!). Your chip just might not be able to run at 266% of rated speed. You could look at manually raising the voltage regulator a wee bit (like they did to get official support for 200MHZ in the RP2040) but that may make things worse if you're already having heat problems somewhere on die.