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README.md

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+# rp-selfdebug
+
 This wraps the CMSIS DAP code in a rust wrapper, and then uses that with the pi
 pico's dbgforce ability to debug core0 from core1 or vice versa.
 
 Make sure you have cloned this repo using submodules.
+
+I created this because I wanted to be able to debug my keyboard firmware
+running USB code without having a debugger attached. The firmware doesn't need
+two cores but it does need to use the USB code, so just using [pico-debug]
+wasn't an option.
+
+## Prior art
+The most obvious inspiration for this is [pico-debug] which would have been a
+good option but the repository was archived and if I was going to use USB, I
+thought I might as well use it in Rust since that's what the rest of the
+keyboard firmware was written in.
+
+I have also been looking at [picoprobe] which was easier to compile as it just
+used cmake and didn't need CrossWorks.
+
+And of course [rust-dap] should also get a mention, which I looked into using,
+but I had problems using it, I suspect the reason was due to it not handling
+error cases correctly and putting `0xFF` into the USB bulk response packet,
+just propagating `Result` out using `?` in the `process` method.
+
+[pico-debug]: https://github.com/majbthrd/pico-debug
+[picoprobe]: https://github.com/majbthrd/pico-debug
+[rust-dap]: https://github.com/ciniml/rust-dap