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. It 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 at 125MHz each and 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**).
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.**
