Hello Lubomir,
Am 07.11.2013 08:57, schrieb Lubomir Popov:
Hi Heiko,
On 07-Nov-13 7:14, Heiko Schocher wrote:
Hello Lubomir,
Am 06.11.2013 14:19, schrieb Lubomir Popov:
On 06-Nov-13 14:12, Nikita Kiryanov wrote:
In drivers/i2c/omap24xx_i2c.c there are a few checks that attempt to detect unconfigured pads for the i2c bus in use. These checks are all in the form of
if (status == I2C_STAT_XRDY) { printf("unconfigured pads\n"); return -1; }
This check seems peculiar to me since the meaning of I2C_STAT_XRDY is that new data is requested for transmission. Why is that indication that the bus is not padconf'd for I2C?
Hi Nikita,
This has been empirically confirmed on OMAP4 and OMAP5. When the pads are not configured, the I2C controller is actually disconnected from the bus. The clock input for its state machine has to come from the bus however due to stretching etc., although it is internally generated. So actually nothing changes within the controller after a transaction attempt is made, and it keeps its initial state with XRDY set only (ready to accept transmit data). I use this as an indicator. Not perfect, but works in most cases.
Thanks for this explanation! Maybe we can document this somewhere in the code?
bye, Heiko
You are right, it would be good to document it. Unfortunately I have not been on the U-Boot wave for some months now due to very heavy engagement with other stuff; have even unsubscribed from the list. I think however that in order to give definite statements and improve the driver, a new round of experiments has to be made to cover the two major types of design flaws (software and/or hardware): incorrect pad configuration, and missing pullups (internal or external). I wrote this driver more that 6 months ago with the goal to have something working properly (the then existing one was, mildly put, not good), and this detection is just a bonus side effect.
In summary, the professional approach would require some more effort, which I'm not sure when I could afford. Otherwise, if just an explanation for the current algo is to be given, no problem - I can just add some comments.
I vote for the professional approach ;-) But if you have no time, and can just send a comment for the current state (maybe with a short summary, what should be done) I am fine with this too!
Thanks!
bye, Heiko