Recreating the Raspberry Pi RP2040 PIO interface in Verilog #RaspberryPi #Verilog #FPGA @lawriegriffiths
FPGA RP2040 PIO is an attempt to recreate the Raspberry Pi RP2040 PIO interface in Verilog.
PIO stands for Programmable I/O, and it is a peripheral that is part of the RP2040 SoC, which is much more flexible than hardware implementations of specific protocols like SPI, I2C, UART etc. It can implement all these protocols and more at high speed and on any GPIO pins.
It runs in up to 8 special processors, known as State Machines, which are programmed in assembler using a machine language designed specifically for fast cycle-accurate I/O. These processors run independently of the main CPUs.
This implementation has been done from the specification, without access to any Raspberry Pi HDL. It is currently incomplete, but some programs run in simulation and on open source FPGA boards.
The current supported boards are the Blackice MX and the Ulx3s. For use by a SoC, e.g. a RISC-V SoC such as SaxonSoc, the appropriate peripheral bus interface would need to be added.
For use from a host processor, such as one running MicroPython, an SPI read/write memory interface could be added. This would be a lot slower than a bus interface but speed is not usually an issue for configuration and control.
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