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Re: I2C bus recovery

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pozz <pozzugno@gmail.com> wrote:
> Il 08/11/2022 23:08, antispam@math.uni.wroc.pl ha scritto:
> > pozz <pozzugno@gmail.com> wrote:
> >> I wanted to implement an I2C bus recovery during initialization. The
> >> reason is well known in literature[1].
> >>
> >> I read the function i2c_generic_recovery[2] of Linux kernel, but I don't
> >> understand one thing.
> >>
> >> The bus recovery is necessary to bring a slave to the end of a byte
> >> transmission that could be interrupted for some reason.
> >> However the slave could be transmitting 0xFF, so why the above function
> >> breaks the loop if SDA is detected high?
> >>
> >>      [Line 620] /* Break if SDA is high */
> > 
> > With normal devices start followed by stop should reset state of the bus.
> > Howere, to send start we need SDA high.  If this is bus with single
> > master SDA should be high at least at the end of byte (bus should
> > flat high as device waits for ACK).
> 
> Do you think that a slave transmitting 0xFF interrupts the transmission 
> in the middle as soon as it detects a falling transition on SDA (STOP)?
> 
> Anyway, in this case the STOP transmission is necessary after reading 
> SDA high. I couldn't find the STOP transmission in the Linux kernel 
> code, only a few clock cycles until SDA is detected high.
> 
> 
> >> Maybe it's better to send 9 clock cycles whatever the level of SDA line.
> > 
> > I am not sure if this helps: writer is supposed to stop seeing new
> > start, so it is not clear if extra clock give anything for writers.
> 
> Yes, if the slave transmitting something stops after seeing a STOP (SDA 
> going low). I don't know it this is a well-known specification and if 
> all the I2C slaves implement this specification correctly.
> 
> 
> > OTOH, if bus is clocked reader could get wrong data, so it seem
> > better to reset bus as soon as possible (that is first time when
> > SDA is high).
> 
> What do you mean with reader? When the bus is stuck, the writer is the 
> slave and the reader should be the master that is trying to recovery the 
> bus, so technically it is not reading anything.
> 
> Are you thinking of a bus with multiple slaves? They shouldn't be 
> reading anything.

If you see low on SDA this could be writer slave sending 0 or
reader slave sending ACK.

-- 
                              Waldek Hebisch

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I2C bus recovery pozz <pozzugno@gmail.com> - 2022-11-08 16:08 +0100
  Re: I2C bus recovery antispam@math.uni.wroc.pl - 2022-11-08 22:08 +0000
    Re: I2C bus recovery pozz <pozzugno@gmail.com> - 2022-11-09 08:32 +0100
      Re: I2C bus recovery Richard Damon <Richard@Damon-Family.org> - 2022-11-10 07:12 -0500
        Re: I2C bus recovery Rick C <gnuarm.deletethisbit@gmail.com> - 2022-11-10 09:06 -0800
        Re: I2C bus recovery pozz <pozzugno@gmail.com> - 2022-11-10 23:39 +0100
      Re: I2C bus recovery antispam@math.uni.wroc.pl - 2022-11-10 17:26 +0000
      Re: I2C bus recovery Michael Schwingen <news-1513678000@discworld.dascon.de> - 2022-11-13 10:52 +0000

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