iCE40 CRAM (Configuration) Programming via FTDI (for IceBreaker, ice40 breakout boards, etc)

ice40_cram_program_ftdi.py

# Example of using PyFTDI to program CRAM on ICE40 FPGA. For example
# if you are using IceBreaker, you'd need to change jumpers to route
# SPI to the FPGA directly instead of the SPI flash.

import pyftdi
from pyftdi.spi import SpiController
import time

class ICE40_ftdi(object):

    def __init__(self, devstr='ftdi://::/1'):
        # Instantiate a SPI controller, reserve two CS pins (ADBUS*3, ADBUS*4)
        spi = SpiController(2)

        # Configure the first interface (IF/1) of the first FTDI device as a
        # SPI master
        spi.configure(devstr)

        # IceBreaker - CS pin on ADBUS*4
        fpga = spi.get_port(cs=1, freq=24E6, mode=0)

        # Get GPIO port to manage extra pins, ADBUS*7 (0x80) as CRST, ADBUS*6 (0x40) as DONE
        gpio = spi.get_gpio()
        gpio.set_direction(0x80 | 0x40, 0x80)

        self.gpio = gpio
        self.fpgaspi = fpga


    def load(self, bspath):
        # Open bitstream
        f = open(bspath, "rb")
        data = f.read()
        f.close()

        fpga = self.fpgaspi
        gpio = self.gpio

        # Start exchange so CS goes low
        fpga.exchange([0], start=True, stop=False)

        time.sleep(0.05)

        # Assert CRST to zero, then set back to one
        gpio.write(0x00)
        time.sleep(0.05)
        gpio.write(0x80)
        time.sleep(0.05) #If FTDI is fast this seems to be needed

        # Stream out - pyftdi barfs if you send everything at once to split
        # it up as needed.
        si = 0
        chunk = 16384
        ei = si + chunk
        nowdone = False

        while True:
            fpga.exchange(data[si:ei], start=False, stop=False)

            if nowdone:
                break

            si = ei
            ei = si + chunk

            if ei > len(data):
                ei = len(data)
                nowdone = True

        # Add extra clock cycles so program starts, otherwise only
        # done pin goes high but isn't running
        fpga.exchange(readlen=400, start=False, stop=True)

        if gpio.read() & 0x40:
            print("DONE Pin High")
        else:
            raise IOError("DONE pin did not go high!")