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Forum Index : Microcontroller and PC projects : Interesting page on bare metal Pico

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lew247

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Joined: 23/12/2015
Location: United Kingdom
Posts: 1702
Posted: 04:20pm 31 May 2023
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Raspberry RP2040 (Pico board) experiences
I don't understand it but others will I guess
and example from the page
  Quote  I wanted to be able to write to the Pico without mounting the fake filesystem or doing anything privileged, so that calls for a libusb userspace program. I started out trying to make a libusb mass storage driver, and I got most of the way there but I just felt so stupid decoding a FAT filesystem just to stream a UF2 file.

So I used the PICOBOOT protocol instead. The RP2040 bootrom supports two USB interfaces -- mass storage and PICOBOOT. PICOBOOT is nice and simple and really not that different from mass storage. So it's easy to support. So now I simply plug it in, run picoprog foo.elf, and a second later it reboots into my program...and then when my program finishes (allows WDT to elapse), it is ready to receive another one! It is so convenient!

That happens to mean I don't need UF2 anymore so this is now completely free of any Raspberry SDK components.

and another
  Quote  Spent a while discovering with the fact that the RP2040 requires 256 byte alignment for the vector table (VTOR), even though the ARMv6-M manual only says 128 byte (but it also says implementation defined). Sigh.

I worked out all the kinks in my second-stage boot loader. So now it can boot from SRAM (blink_sram.elf), a flash loader that copies .text and .rodata into SRAM and then executes from SRAM (blink_fl.elf), or in XIP mode where it accesses .text and .rodata directly from flash (blink_xip.elf). So the C blinky is now roughly a minimal complete SDK. It now has everything I wish had come in the box with the Pico:
 
JohnS
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Joined: 18/11/2011
Location: United Kingdom
Posts: 3998
Posted: 01:39pm 02 Jun 2023
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Thanks for posting that.

John
 
Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 4854
Posted: 02:38pm 02 Jun 2023
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hdmi-vga

cheaper than any pico, and you can even insert audio
PicomiteVGA PETSCII ROBOTS
 
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