• Jean Delvare's avatar
    i2c-algo-bit: Implement a 50/50 SCL duty cycle · 424ed67c
    Jean Delvare authored
    The original i2c-algo-bit implementation uses a 33/66 SCL duty cycle
    when bits are being written on the bus. While the I2C specification
    doesn't forbid it, this prevents us from driving the I2C bus to its
    max speed, limiting us to 66 kbps max on standard I2C busses.
    
    Implementing a 50/50 duty cycle instead lets us max out the bandwidth
    up to the theoretical max of 100 kbps on standard I2C busses. This is
    particularly important when large amounts of data need to be transfered
    over the bus, as is the case with some TV adapters when the firmware is
    being uploaded.
    
    In fact this change even allows, at least in theory, fast-mode I2C
    support at 125, 166 and 250 kbps. There's no way to reach the
    theoretical max of 400 kbps with this implementation. But I don't
    think we want to put efforts in that direction anyway: software-driven
    I2C is very CPU-intensive and bad for latency.
    
    Other timing changes:
    * Don't set SDA high explicitly on error, we're going to issue a stop
      condition before we leave anyway.
    * If an error occurs when sending the slave address, yield the CPU
      before retrying, and remove the additional delay after the new start
      condition.
    Signed-off-by: default avatarJean Delvare <khali@linux-fr.org>
    424ed67c
i2c-algo-bit.h 2.09 KB