Hi Krzysztof: > "Mark M. Hoffman" <mhoffman at lightlink.com> writes: > > SCL and SDA must be pulled high by hardware. If a driver inits to > > setting them low, that's a bug in the driver. * Krzysztof Halasa <khc at pm.waw.pl> [2006-06-11 00:27:14 +0200]: > Thanks for your response. > > The question is rather who inits the lines: a) the hw driver, > b) the I2C algorithm driver. > > With a) every hw driver has to know how to init them (duplicated > code but there might be positive side). > > With b) I2C algorithm driver inits the lines and hw driver > doesn't worry about but it might have some limitations such > as unknown SCL state. > > I understand the current case is a) - right? I think it should be, yes. > The other question is _how_ to init the lines. There are 4 possible > hardware initial conditions: > > SCL SDA > a) 0 0 (outputs zeroed by default) > b) 0 1 (uncommon but may be left in this state by previous operations) > c) 1 0 (ditto) > d) 1 1 (I/O lines configured as input by default) > > The internal state of devices connected to the bus is potentially > unknown. Some implementations just start with STOP to eliminate > this problem, I don't know what Linux driver is supposed to do. If you can read the line state, then yes... I would detect which of the above four states you're in, and generate a STOP condition for a, b, and c: a) setscl(1), setsda(1) b) setsda(0), setscl(1), setsda(1) c) setsda(1) If you can't read the line state... well, that's not actually a proper I2C bus anyway. At that point I suggest 'whatever works'. But even if you need to generate a 'null transfer' (prohibited by spec) to get reliable operation... that doesn't belong in the algorithm driver. > (Other implementation I know are rather specialized and thus they > know their hardware init state, Linux I2C algorithm handles many > devices with potentially different initial state of hardware lines). > > > To summarize questions: > - is it the hw driver who has to init the bus > - how to init the bus (depending on init state) Regards, -- Mark M. Hoffman mhoffman at lightlink.com
