Update RP2040 memory.x

[jamesmunns]

The RP2040 has 264KiB of memory, not 256KiB.

Citation: https://www.raspberrypi.com/documentation/microcontrollers/rp2040.html#technical-specification

264kB on-chip SRAM in six independent banks

[lulf]

Good catch, thanks! Could you update these too?

• boot/bootloader/rp/memory.x
• boot/application/rp/memory.x

[Athorus]

Above 0x20040000, the 8 KB of SRAM are not striped ! So I am not sure it is a good idea to mix non striped SRAM with striped SRAM.
See page 25 of the datasheet https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf

[jamesmunns]

@Athorus that's fair! on one hand: using unstriped ram primarily for the core might be good, if it is uncontended with DMA access.

On the other hand: we have no control over that for user code, and if we only give 4K of stack for each core, that might not reasonably be enough.

[Athorus]

With 256K, at the end of the program I got as expected :
(HOST) INFO program has used at least 26.55/141.34 KiB (18.8%) of stack space

But with 264K I got this strange message !
(HOST) WARN program has used at least 4.00/4.00 KiB (100.1%) of stack space

In both cases, the program seems to work fine

[Dirbaio]

Good catch, thanks! Could you update these too?

* `boot/bootloader/rp/memory.x`

* `boot/application/rp/memory.x`

ping @jamesmunns :)

[Dirbaio]

Above 0x20040000, the 8 KB of SRAM are not striped ! So I am not sure it is a good idea to mix non striped SRAM with striped SRAM. See page 25 of the datasheet https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf

examples are supposed to be simple, and "the default memory.x allows me to use all RAM" makes a lot of sense for examples. The datasheet specifically says the ram is laid out like that so you can pretend it's a contiguous 264k block. for the majority of applications it's likely to increase perf (moves core activity to sram4-5, while dma is most likely to use sram0-3). and only for very particular circumstances (several DMAs adding up more than 1 word/cycle out of stack) it might reduce perf. So IMO it's worth doing this change.

With 256K, at the end of the program I got as expected : (HOST) INFO program has used at least 26.55/141.34 KiB (18.8%) of stack space

But with 264K I got this strange message ! (HOST) WARN program has used at least 4.00/4.00 KiB (100.1%) of stack space

In both cases, the program seems to work fine

This is knurling-rs/probe-run#415 (the regions are separate in the probe-rs target definition). it's a bit moot now that probe-run is deprecated though.

[Dirbaio]

thank you!

[Athorus]

This is knurling-rs/probe-run#415 (the regions are separate in the probe-rs target definition). it's a bit moot now that probe-run is deprecated though.

Shoud I use probe-rs instead of probe-run ?

[Dirbaio]

yes https://ferrous-systems.com/blog/probe-run-deprecation/