This Git repository contains a Micro-SDR implementation, based on a RP2040 Pi Pico. The project is highly experimental, foremost intended to investigate how the Pico HW and SDK work with an application like this. Also it is a platform to experiment with digital signal processing techniques. The repo contains the code for an experimental implementation of the control and signal processing for a QSD/QSE based transceiver.
The platform used is a Pi Pico module with an RP2040 processor. This processor has dual cores, running default at 125MHz each, and a very configurable I/O which eases the HW design.
The software is distributed over the two cores: *core0* takes care of all user I/O and control functions, while *core1* performs all of the signal processing. The *core1* functionality consists of a TX-branch and an RX-branch, each called from a function that waits for inter-core FIFO words popping out. This happens every 16usec, because on *core0* a 16usec timer callback ISR pushes the RX/TX status into that FIFO. Hence the signal processing rythm on *core1* effectively is 62.5kHz.
On *core1* the three ADC channels are continuously sampled at maximum speed in round-robin mode. Samples are therefore taken every 6usec for each channel, maximum jitter between I and Q channels is 4usec, which has a negligible effect in the audio domain.
On *core0* the main loop takes care of user I/O, all other controls and the monitor port. There is also a LED flashing timer callback functioning as a heartbeat.
The Pico controls an Si5351A clock module to obtain the switching clock for the QSE and QSD. The module outputs two synchronous square wave clocks on ch 0 and 1, whith selectable phase difference (0, 90, 180 or 270 degrees). The clock on ch2 is free to be used for other goals. The module is controlled over the **i2c0** channel.
The display is a standard 16x2 LCD, but with an I2C interface. The display is connected through the **i2c1** channel, as well as the bus expanders for controlling the various relays.
Please refer to https://github.com/ndabas/pico-setup-windows/releases where the latest installer can be downloaded (e.g. **pico-setup-windows-0.3-x64.exe**).
You can upgrade the SDK to the latest version by replacing the complete **$PICO/pico-sdk** folder with the newer version. The latest version is on Github: https://github.com/raspberrypi/pico-sdk (download code as zip, extract the **pico-sdk-master** folder from it, rename it to **pico-sdk** and use it to replace the original)
Before doing any building you need to adapt the file **$PICO/uSDR-pico/CMakeLists.txt**, using your favourite editor, to reflect your own directory structure. Also, select whether you want **stdio** to use the UART on pins 1 and 2 or the USB serial port. The monitor terminal is on **stdio**.
In **$PICO/** you will find a command to start a Developer Command Prompt (*DCP*, like a "DOS box"), make sure to use this one instead of any other DOS box. Within this *DCP* all environment settings have been properly pre-set to enable building.
In the *DCP* window, chdir to the **build** folder and execute: **cmake -G "NMake Makefiles" ..** (do not forget the trailing dots).
Now you have initialized the make environment (for *nmake*) and by executing **nmake** in that same **build** folder, all SDK libraries and finally the Pi Pico loadable file **uSDR.uf2** will be created.
Rebooting the Pico while the bootsel button is pressed will open a file explorer window with the Pico shown as a Mass Storage Device (e.g. drive E:). Moving the binary to the Pico is as easy as dragging and dropping this uf2 file into that MSD.
The folder **$PICO/docs** also contains some manuals, of which the *C-SDK description*, the *RP2040 datasheet* and the *Pico Pinout* are absolute must-reads when you start writing software.
**The code and electronic designs as well as the implementations presented in this repository can be copied and modified freely, for non-commercial use.
Use for commercial purposes is allowed as well, as long as a reference to this repository is included in the product.**
