Raspberry Pi Pico frequency divider
Divides the input frequency by factor 10^7 (or other), 10MHz to 1Hz using PIO. System clock can to be driven from 10MHz external clock through GPIO. Based on the pio_blink example.
For using external clock reference as system clcok connect 10 MHz 0-3.3V input signal to GPIO20 (pin 26). Output signals will be following:
- OUT_A - GPIO17 (pin 22) - 1 PPS, 10 ms long pulses,
- OUT_A - GPIO25 (onboard LED),
- OUT_B - GPIO18 (pin 24) - 100 kHz 0-3.3V square wave,
- UNSYNC - GPIO21 - unsynced 1 PSS from RP2040 clock divider.
To use the onboard TXCO as system clock, comment out EXT_CLK.
GPIO19 is used to syncrhonized outputs to external sync signal. If synchronization not required connect GPIO20 and GPIO19 for immediate startup. Synchronization is done only once upon start. After that the outputs are directed only by system clock. The output can be fine tuned with 100ns steps (@10MHz system clock) to sync signal with SYNC_TUNE.
This is an example to use the internal PWM module to count pulses and generate output divided frequency. However the output pins are also driven by clk_sys. So using the defualt 125 MHz internal clock frequency leads to 8ns jitter on the output pulses.
Connect the Pico while holding down the button on the Pico board to USB. Drag and drop the *.uf2 file to Pico board.
In case of problems consult the great Raspberry Pi Pico Getting Started Guide.
Get you environment ready by installing the toolchain.
Setup local environment variables
export PATH="$PATH:/Applications/microchip/xc8/v2.31/bin"
export PICO_TOOLCHAIN_PATH=/Applications/ARM/bin
export PICO_SDK_PATH=<pico-sdk>
Change to build directory
cd ./build
Run commands to compile and build
cmake ../
make
After that you should find picoDIV.uf2 file in the build directory that can be used to program your board.