Booting the RP2350 from UART

One could also send a binary stub that sets up fast CPU clock speed and decompresses the rest of the firmware at the RP2350 side. Should be even faster.<p>Just like old C64 decrunchers and Amiga PowerPacker. Or Fabrice Bellard&#x27;s LZEXE. (Is there anything that guy did NOT write?!)

This is one of the tricks to enable using both QSPI slots for PSRAM instead of the typical FLASH+PSRAM.<p>This is great for making audio modules, where the firmware is be small and operates on a big audio buffer. Since the biggest available PSRAM chips are 8MB, this combined 16 MB could hold around 3 minutes of mono 16-bit audio, which allows for a very nice multi track looper.<p>Another way (in case there&#x27;s no other MCU to help with uart bootstrap) would be to add a logic chip to multiplex the CS line between Flash and the first PSRAM - copy firmware to flash and then switch to using ram.

This is awesome. I&#x27;ve had similar ideas but wasn&#x27;t able to do any prototyping yet as I only have Pico 2 boards that don&#x27;t expose the CSn pin in the pinout.<p>Rather than UART booting every time I thought it might be nice to use UART Boot just as a way to deliver the firmware update to the sub chip - so the UART image you load would just be a program that accepts a larger image (over UART again) and would write to the flash for subsequent boots. I think that would get around the SRAM and boot time downsides the author mentioned. Is there a reason this might not work?

Are there any off-the-shelf hobbyist boards that expose QSPI CSn (pin 75 on the RP2350B?) and QPI_SD1-3 signals to a header or pin? Doesn&#x27;t seem like the official Pico 2 or the Adafruit or Pimoroni versions of the Pico 2 expose access to these signals without modifying the board, which most people won&#x27;t be able to do.

In principle, you could boot the RP2040 over SWD. It&#x27;d be much more difficult to code, but the possibility is there...

The CH32V003 has also a UART bootloader, but for some reason there is no open source command line client to do something with it. WCH has a Windows GUI though.

There&#x27;s nothing speaking &quot;version 1.0&quot; more than a bunch of stuff just manually soldered as piggyback over other components of the board :D<p>Thanks for the writeup.

this is also how some BLE controller boot.