PSRAM crashes on 252MHZ overclock (set in code , not from the IDE menu)

[Macrosii]

High. I am using a PICO2 Plus with PSRAM and running the Adafruit "PicoDVI" library. This library over-clocks the processor in code to 252Mhz to get the PIO outputting at the correct speed for DVI. I tried adding some PSRAM stuff (fame buffer takes up a lot of the normal RAM) and I am experiencing crashes. Is the PSRAM access speed set up from the IDE menu ?

[earlephilhower]

PSRAM is driven from clk_sys, so if you change that then you need to change the divider or it'll go out of spec and the PSRAM chip will probably go very badly. See:

arduino-pico/cores/rp2040/psram.cpp

Lines 198 to 231 in ca30518

	static void __no_inline_not_in_flash_func(set_psram_timing)(void) {
	// Get secs / cycle for the system clock - get before disabling interrupts.
	uint32_t sysHz = (uint32_t)clock_get_hz(clk_sys);
	// Calculate the clock divider - goal to get clock used for PSRAM <= what
	// the PSRAM IC can handle - which is defined in SFE_PSRAM_MAX_SCK_HZ
	volatile uint8_t clockDivider = (sysHz + SFE_PSRAM_MAX_SCK_HZ - 1) / SFE_PSRAM_MAX_SCK_HZ;
	uint32_t intr_stash = save_and_disable_interrupts();
	// Get the clock femto seconds per cycle.
	uint32_t fsPerCycle = SFE_SEC_TO_FS / sysHz;
	// the maxSelect value is defined in units of 64 clock cycles
	// So maxFS / (64 * fsPerCycle) = maxSelect = SFE_PSRAM_MAX_SELECT_FS64/fsPerCycle
	volatile uint8_t maxSelect = SFE_PSRAM_MAX_SELECT_FS64 / fsPerCycle;
	// minDeselect time - in system clock cycle
	// Must be higher than 50ns (min deselect time for PSRAM) so add a fsPerCycle - 1 to round up
	// So minFS/fsPerCycle = minDeselect = SFE_PSRAM_MIN_DESELECT_FS/fsPerCycle
	volatile uint8_t minDeselect = (SFE_PSRAM_MIN_DESELECT_FS + fsPerCycle - 1) / fsPerCycle;
	// printf("Max Select: %d, Min Deselect: %d, clock divider: %d\n", maxSelect, minDeselect, clockDivider);
	qmi_hw->m[1].timing = QMI_M1_TIMING_PAGEBREAK_VALUE_1024 << QMI_M1_TIMING_PAGEBREAK_LSB | // Break between pages.
	3 << QMI_M1_TIMING_SELECT_HOLD_LSB | // Delay releasing CS for 3 extra system cycles.
	1 << QMI_M1_TIMING_COOLDOWN_LSB | 1 << QMI_M1_TIMING_RXDELAY_LSB |
	maxSelect << QMI_M1_TIMING_MAX_SELECT_LSB | minDeselect << QMI_M1_TIMING_MIN_DESELECT_LSB |
	clockDivider << QMI_M1_TIMING_CLKDIV_LSB;
	restore_interrupts(intr_stash);
	}

[Macrosii]

Many Thanks. That did it, I changed the clock divider and it running ok .

[FreddyVRetro]

252MHz is maybe Ok, but above 266MHz, need to change other things (rxdelay to 4 for example)
Is there somewhere a guide for all the frequency ?
Any strong RAM Test code somewhere ?