Cannot transfer more than 255 bytes via SPIM0 on nrf52840

[Jiacheng Guo]

When trying to write a long buffer to external flash via SPIM0, I found the TXD.MAXCNT is limited to 255.

I'm directly manipulation the registers. When I wrote 256 into TXD.MAXCNT and read it,  I got 0 instead.

The datasheet shows this register should be 16 bit.

[Jørgen Holmefjord]

Hi,

Which revision of the chip are you using? This should work on rev 1 chips. I tested on nRF52840 PDK v0.9.0 vs nRF52840 DK v1.0.0:

$ nrfjprog --memwr 0x40003548 --val 256
Parsing parameters.
Writing.

$ nrfjprog --memrd 0x40003548
0x40003548: 00000000                              |....|

$ nrfjprog --memwr 0x40003548 --val 256
Parsing parameters.
Writing.

$ nrfjprog --memrd 0x40003548
0x40003548: 00000100                              |....|

Best regards,
Jørgen

[Jiacheng Guo]

I'm using v0.9.2

Serial number: 683055308

So it's supposed to be a bug in the early version of chips?

[Jørgen Holmefjord]

Not a bug, but a limitation/not implemented feature in the engineering revisions. Note that engineering revision chips are not final products and will have issues and missing features compared to the final product. 

The limitation is documented in nRF52840 OPS v0.5.1.1 in the SPIM instances section:

[jiri.husak]

Hello,

could you please advice which Engineering has this "limitation"? All types between engineering A-C? Because in other thread I can read that the engineering C is equal to revision 1. Please see answer here https://devzone.nordicsemi.com/f/nordic-q-a/38133/nrf52840-versions/147098#147098.

Thanks for clarification.

Regards,

Jiri

[Jørgen Holmefjord]

The limitation is only present in Engineering A revision. I just verified that the register is 16 bits in Engineering B and C (v0.11.0 and v0.12.0 PDKs).