RP2350 Initial Support

[haydenridd]

The RP2350 is now running Zig! Credit to @timsavage for some of the initial work in porting.

Restructuring

Some housekeeping for the new chip:

• port/raspberrypi/rp2040 has become port/raspberrypi/rp2xxx since both chips are under the same HAL
• examples/raspberrypi/rp2040 has similarly become examples/raspberrypi/rp2xxx
• compatibility.zig was added to the HAL for determining which chip you're using at compile time

Apologies as this makes the diffs horrendous, but if you have a good diff tool like BeyondCompare it's fairly easy to align the renamed folders to see what changed.

Boot Rom

Unlike the RP2040, there is no longer a need to write your own "stage 2 bootloader" that fits in 256 bytes and has a special header. They've changed things around quite a bit and added lots of functionality to the ROM code that runs on boot. Way too much to go over here, but the TLDR is the boot ROM looks for metadata in your binary that's sitting in flash to determine if/how to run it. I've added a "bare minimum dumb config" that essentially just says "run this binary sitting in flash please". Chapter 5 of the data sheet (Bootrom) is well worth the read as there's some pretty cool stuff we could do with this metadata in the future.

HAL Integration

Zig actually made this part pretty pleasant. You'll see a general pattern of:

switch (get_cpu()) {
        .RP2040 => {},
        .RP2350 => {},
    },

There are two methodologies I've used a bit of both of:

• Swap out some things "as needed" in the same file if core functionality is pretty similar (see gpio.zig)
• Separate the two chip's unique functionality into two separate files as there are enough differences to warrant this (see clocks.zig)

Both have their pros and cons, but overall I'm pretty happy with the readability and intuitiveness of both.

Progress

So far I've ported + tested the following from the HAL:

• clocks.zig
• gpio.zig
• pll.zig
• resets.zig
• time.zig

Examples

I've modified the examples so that there are:

• RP2040 only examples (most of them right now due to HAL compatibility)
• RP2350 only examples (none yet but you could imagine using the new HSTX peripheral would go here)
• Chip agnostic examples (in the future ideally most of them fall under this category)

This is a pretty easy way to see RP2350 port progress as well, since any example that runs on the RP2350 essentially means I've run that example on my own hardware and made sure it works.