QSPI Flash memory size

[CFourie]

Hi everyone,

I'm looking to add some storage space to a project and I'm looking at the GD25Q16. I know this chip works since it is used on the Adafruit NRF52840 Feather.

I would like a little (a lot) more space for testing purposes and the GD25LQ256 caught my eye - will this work? Spec-wise it seems similar, except for having 16x the storage space. Is there a limit to how much memory the NRF52840 can access?

The other option is soldering a MicroSD directly to the board - since for some reason you don't get SMD Micro SD cards.

Kind regards,

Chris Fourie

[wpaul]

There are two ways to perform accesses to QSPI devices:

1) Issue read/write/erase commands directly via the QSPI controller

2) Map the flash into the address space, such that you can read it or execute code from it just like with the on-board 1MB flash

This second option is called eXecute In Place (XIP) mode. If you download a copy of the nRF52840 Product Specification (reference manual), and look at the memory map in section 4.2.3, you'll see there is a range allocated for XIP. You will note that it's only 128MB in size.

When using direct accesses via the QSPI controller, I think the limiting factor would be the largest offset size you can use. I dimly remember that there's an option to choose between 24-bit and 32-bit addressing mode. For larger parts you would have to use the latter.

Assuming you do use 32-bit addressing, then I think think you'd be limited to 4GB parts.

But for XIP, you would not be able to map more than 128MB.

-Bill

[CFourie]

Thank you, I'll have to investigate this a little bit more. It is my first foray (apart from some assembly programming) into programming outside the Arduino environment, so a lot of new things to learn.

I did see last night that the NRF52840 DK has a 64MB chip onboard, so I'll be looking into the examples to see how that memory was accessed and how easy it is to replicate.

[bjorn-spockeli]

I second what wpaul stated in his answer. 

I recommend taking a look at our QSPI Example to see how to do 1) and take a look at QSPI bootloader Example to see how to do 2).

Best regards

Bjørn 

[wpaul]

Just one clarification: the QSPI flash chip on the DK board is a Macronix MX25R6435F. The capacity of this part is 64 megaBITS, which works out to 8 megaBYTES. You need to watch out for the lower case 'b' instead of upper case 'B' in the specs. The datasheet for the part is here:

www.macronix.com/.../MX25R6435F, Wide Range, 64Mb, v1.4.pdf

-Bill

[CFourie]

Thank you, I'll give both a go.