I made a custom PCB with the NRF52840-CKAA and the same 8MB flash memory chip as the PCA10056 NRF528040DK
I used the MX25R6435FZAIL0 because the MX25R6435FZNIL0 was not available from LCSC
The only difference is the package code ("M2" instead of "ZN")
I altered the NCS 2.6.0 usb_mass_storage example to change the pins to match the ones I used on my PCB.
I could not get it to work so I suspected the chip was not connected properly.
So I made a test using the nrf_qspi peripheral directly and eventually managed to confirm single wire mode worked. Later I was able to set the QuadEnable bit in the MX25 status register to get 4-wire mode working. So that suggests the chip is connected
I then went back to the usb_mass_storage example and located the driver code and found that it failed to read the JEDEC ID in qspi_init (line 1063 in nrf_qspi_nor.c). It got zeros instead of the JEDEC code. I stepped through the code and discovered that it worked. But only if I single stepped in the debugger. if I ran the code then it still failed.
I then found that if I introduce a delay between the calls to nrf_qspi_task_trigger, then it works
I also found the "rx_delay" dts parameter, and I tried setting it to 250 (almost the maximum 255), but it didn't work
I am struggling to understand what might be causing this.
I'm reaching out to see if this "rings any bells" with one of your developers.
The current "fix" is obviously a hideous hack, and I do not understand why I need to add this delay. I believe the driver code only failed to read the JEDEC code, but perhaps it impacts other communications that I've not encountered. So I will have to find a better solution.
I also tried to run the NCS2.8.0 usb mass storage example but it doesn't compile with the nrf52840DK (PCA10056)
Any suggestions are greatly appreciated.
Kind regards,
-Jason
