When you want to deploy something new (or a new version of something) to a Pi Pico or 2040 Stamp, you need a way to put the device in bootsel mode, which will allow you to copy a new firmware image onto the device.
The Round Stamp Carrier I’ve been using a lot lately lacks a bootsel button. To manually reset the unit, I had to use alligator clips to bridge the bootsel pin to ground, and simultaneously hit the onboard reset button. This was pretty fiddly and often took a few tries to do right.
I wanted a way to do this in software without adding any new buttons. Firmware images like MicroPython support hitting the built-in reset button twice to enter bootsel mode. I did some searching to figure out how they did this, and it turns out it’s simple.
The Pico SDK, includes this comment, which suggests that all you need to do is link a particular library. Looking at the CMakeLists.txt file in that directory, we see that the library is available under the name pico_bootsel_via_double_reset.
We can add this to our linked libraries in our own CMakeLists.txt file, so that we have a block that looks something like:
target_link_libraries(
${NAME}
pico_stdlib
pico_neopixel
pico_bootsel_via_double_reset
)
This example is for a project where I’ve set a variable NAME for the name of the project/binary. Once I added the last entry, recompiled, and performed one last manual install, my firmware now includes support for double-tapping the reset button to enter bootsel mode.
If you’re looking for remote options, there are a few. I have a picoprobe, if you connect that to the SWD pins on the chip, you can reset (and install new firmware) using openocd.
There are also several methods for entering bootsel mode by connecting to the device over USB, which you can read about in this forum post.
If you’re iterating on your firmware design and looking for easy ways to reset, I hope this was helpful.