Add support for pinning XIP SRAM

[will-v-pi]

Adds support for pinning XIP SRAM in a load map, and allows use of XIP SRAM in flash binaries

[lurch]

For people like me who have no idea what "pinning XIP SRAM" is about, maybe it's worth adding a comment pointing to 5.9.3.2.1. in the RP2350 datasheet? 😉

[lurch]

"If, however, you have a non-flash binary with code or data in the XIP RAM address space, then you need to add a special
LOAD_MAP entry to indicate to the bootrom that the XIP contents should be pinned."
Does that imply that you could infer from the binary itself whether the XIP RAM needs to be pinned, rather than requiring an additional CLI flag?

[will-v-pi]

"If, however, you have a non-flash binary with code or data in the XIP RAM address space, then you need to add a special LOAD_MAP entry to indicate to the bootrom that the XIP contents should be pinned." Does that imply that you could infer from the binary itself whether the XIP RAM needs to be pinned, rather than requiring an additional CLI flag?

Not necessarilly, because you could choose to pin manually only the region you want before loading your code/data into XIP SRAM, rather than having the bootrom pin the whole thing, in order to minimise the flash performance loss that comes from pinning XIP SRAM.

[lurch]

you could choose to pin manually only the region you want before loading your code/data into XIP SRAM, rather than having the bootrom pin the whole thing, in order to minimise the flash performance loss that comes from pinning XIP SRAM.

Okay. So is the --pin-xip-sram flag being added here doing the "Pin all of XIP SRAM on load" behaviour?

[will-v-pi]

For people like me who have no idea what "pinning XIP SRAM" is about, maybe it's worth adding a comment pointing to 5.9.3.2.1. in the RP2350 datasheet? 😉

That section of the datasheet is currently incorrect (I have a PR open to fix it), but more generally picotool doesn't currently refer to the datasheet and instead assumes prior knowledge of the bootrom functionality (eg signing and hashing, what a load map is, etc), as that stuff is documented elsewhere

[will-v-pi]

you could choose to pin manually only the region you want before loading your code/data into XIP SRAM, rather than having the bootrom pin the whole thing, in order to minimise the flash performance loss that comes from pinning XIP SRAM.

Okay. So is the --pin-xip-sram flag being added here doing the "Pin all of XIP SRAM on load" behaviour?

Yes, it's adding a load map entry to ask the bootrom to do that

[lurch]

Hmmm, very weird that the "Test Build Examples" jobs have suddenly decided to start failing 😕 It's complaining about a missing file but I don't think that any of the relevant repos have changed recently?

[will-v-pi]

BTStack has been bumped in the SDK but not yet in pico-examples, which is causing the failure

[lurch]

BTStack has been bumped in the SDK but not yet in pico-examples, which is causing the failure

Ahhhh! Thanks 😀