nRF51822 memory layout and compilation

RE: nRF51822 memory layout and compilation

Susheel Nuguru — Mon, 17 Apr 2023 07:14:06 GMT

[quote user="bojan"]Also, if our code does not fit in the Application area, why don't we get the error during the compilation and linking process that the code is too big? Are our settings of the Application and Bootloader linkers OK? Do we need to specify something else?[/quote]

It seems like the way it is designed, and the memory pointers being use, the linked is not able to figure out that application is spilling into the application reserved space. The virtual pages number and size seems to be a runtime evaluation thing and not a link time.

RE: nRF51822 memory layout and compilation

bojan — Mon, 17 Apr 2023 06:27:01 GMT

Thanks for the clarifications, Susheel Nuguru .

It is now clear to us that we would need to set:

#define FDS_VIRTUAL_PAGE_SIZE 256

if we want the Application data flash area of 3KB.

Now, if we create a new DFU image with such a setting (3KB Application data area) and update the nRF51 that runs with the old settings (12KB Application data area), would that update take effect without bricking the device?

Also, if our code does not fit in the Application area, why don't we get the error during the compilation and linking process that the code is too big? Are our settings of the Application and Bootloader linkers OK? Do we need to specify something else?

Regards,
Bojan.

RE: nRF51822 memory layout and compilation

Susheel Nuguru — Thu, 13 Apr 2023 11:33:35 GMT

The size that you are giving in FDS_VIRTUAL_PAGE_SIZE is in words. That is 1024 words is equal to 4096 bytes.

4906 bytes = 4 Physical pages on nRF51.

Setting FDS_VIRTUAL_PAGES as 3 means that you are reserving 3*1024 words = 3072 words = 12,288 bytes = 12 physical pages for FDS.

I think your main confusion was thinking that FDS_VIRTUAL_PAGE_SIZE size is in bytes, but the size is in words as described clearly in the documentation. (word = 4 bytes). As developers we are used to deal with sizes as bytes so, I understand your confusion :)

RE: nRF51822 memory layout and compilation

Susheel Nuguru — Tue, 11 Apr 2023 10:18:04 GMT

Hi,
We just came back from Easter vacation and that was the reason for no response from out end. Due to very high traffic during this period on devzone and fewer people working this week, we did not manage to assign this to an expert yet. We will look into this as soon as possible, but please expect more delays the first two days. Thanks for your patience so far.