I2C BitBanging over LiteX-Server

i2c_bitbanging.py

import time

# I2C Constants ------------------------------------------------------------------------------------

I2C_SCL    = 0x01
I2C_SDAOE  = 0x02
I2C_SDAOUT = 0x04
I2C_SDAIN  = 0x01

def delay_us(d):
    time.sleep(d/1000000)

def delay_ms(d):
    time.sleep(d/1000)

I2C_DELAY = 1
I2C_WRITE = 0
I2C_READ  = 1

# SFP I2C -----------------------------------------------------------------------------------------

class SFPI2C:
    def __init__(self, regs):
        self.regs = regs

        self.started = 0

        self.regs.cpri0_i2c_w.write(I2C_SCL)
        # Check the I2C bus is ready
        while(not (self.regs.cpri0_i2c_r.read() & I2C_SDAIN)):
            delay_ms(1)

    # I2C bit-banging functions from http://en.wikipedia.org/wiki/I2c
    def read_bit(self):

        # Let the Slave drive data
        self.regs.cpri0_i2c_w.write(0)
        delay_us(I2C_DELAY)
        self.regs.cpri0_i2c_w.write(I2C_SCL)
        delay_us(I2C_DELAY)
        bit = (self.regs.cpri0_i2c_r.read() & I2C_SDAIN)
        self.regs.cpri0_i2c_w.write(0)
        return bit

    def write_bit(self, bit):
        if bit:
            self.regs.cpri0_i2c_w.write(I2C_SDAOE| I2C_SDAOUT)
        else:
            self.regs.cpri0_i2c_w.write(I2C_SDAOE)
        delay_us(I2C_DELAY)
        # Clock stretching
        self.regs.cpri0_i2c_w.write(self.regs.cpri0_i2c_w.read() | I2C_SCL);
        delay_us(I2C_DELAY)
        self.regs.cpri0_i2c_w.write(self.regs.cpri0_i2c_w.read() & ~I2C_SCL);

    def start_cond(self):
        if self.started:
            # Set SDA to 1
            self.regs.cpri0_i2c_w.write(I2C_SDAOE| I2C_SDAOUT);
            delay_us(I2C_DELAY)
            self.regs.cpri0_i2c_w.write(self.regs.cpri0_i2c_w.read() | I2C_SCL);
            delay_us(I2C_DELAY)
        # SCL is high, set SDA from 1 to 0
        self.regs.cpri0_i2c_w.write(I2C_SDAOE| I2C_SCL)
        delay_us(I2C_DELAY)
        self.regs.cpri0_i2c_w.write(I2C_SDAOE)
        self.started = 1

    def stop_cond(self):
        # Set SDA to 0
        self.regs.cpri0_i2c_w.write(I2C_SDAOE)
        delay_us(I2C_DELAY)
        # Clock stretching
        self.regs.cpri0_i2c_w.write(I2C_SDAOE| I2C_SCL)
        # SCL is high, set SDA from 0 to 1
        self.regs.cpri0_i2c_w.write(I2C_SCL)
        delay_us(I2C_DELAY)
        self.started = 0

    def write(self, byte):
        for bit in range(8):
            self.write_bit(byte & 0x80)
            byte <<= 1
        ack = not self.read_bit()
        return ack

    def read(self, ack):
        byte = 0
        for bit in range(8):
            byte <<= 1
            byte |= self.read_bit()
        self.write(not ack)
        return byte