icefm - Proof of concept FM on the Lattice iCEstick

icefm is a basic proof of concept FM transmitter written in SpinalHDL and targetting the Lattice iCEstick. Any other Lattice FPGAs which have PLLs should be easy to support.

Theory of Operation

The iCEstick has one PLL on board. The icepll program from the amazing icestorm software package can generate Verilog modules which instantiate the PLL.

SpinalHDL has a facility for importing arbitrary Verilog - the BlackBox component.

This project simply bridges these two technologies. The result is a routing of the PLL output frequency to a GPIO pin.

Example Verilog files are included which target 109.5MHz.

Requirements

The scripts assume the following are present:

• sbt
• yosys
• nextpnr-ice40
• icepack

Building

1. Generate PLL.v
   1. Run gen-pll.sh or otherwise run icepll to generate the PLL module with the expected name of PLL.v
2. Generate PLLSoc.v
   1. Load the project in IDEA and run the PLLVerilog target in PLL class.
   2. Alternatively, run sbt "runMain icefm.PLLVerilog"
3. Synthesize and route by running synth.sh or your process of choice.