Dear Lothar Waßmann, > Hi, > > Marek Vasut writes: > > Hi Lothar, > > > > > The timing calculation is rather bogus and gives extremely wrong > > > results for higher frequencies (on an i.MX28). E.g. instead of 400 kHz > > > I measured 770 kHz. > > > > > > Implement a calculation that adheres to the I2C spec and gives exact > > > results for I2C frequencies from 12.56 kHz to 960 kHz. > > > > > > Also the bus_free and leadin parameters are programmed according to > > > the I2C spec for standard and fast mode. > > > > I suspect the resulting speed is heavily dependent on hardware properties > > of the bus. Did you have a chance to check it with a scope? I will try > > to recheck on other boards next week. > > Of course I did! I found the DS1339 RTC not working on our hardware > with the I2C clock frequency set to 400kHz and then checked the bus > timing. I found the SCL frequency to be 770kHz instead of 400kHz and > 113kHz instead of 100kHz. > On what hardware did you do your measurements? MX28EVK and M28EVK. > The fancy constants -2 and -7 in the calculation were derived from > measuring the clock low and high time with low_count and high_count > set to 1 and measuring the actual timing of the signal. > The clock frequeny in this setup is 2.18 MHz corresponding to 11 clock > cycles of the 24MHz clock. The LOW time was about 140ns and the HIGH > time 318ns corresponding to 3 and 8 (instead of 1) clock cycles. > > These constants could be different for different SoCs (i.MX23). > But I don't have any hardware to verify that. I can check it for you on MX23 next week, I have two boards with that chip with well accessible I2C. I am not in the office now, so this will have to wait until next week. btw offtopic, I will at least try to fix the PIO in the meantime. > Maybe some guru from Freescale can comment on this and perhaps > document the relationship between the register contents and the actual > timing. Ok, you're taking a third stab at getting FSL to explain how to configure arbitrary clock speeds on the MXS I2C. Good luck ;-D Best regards, Marek Vasut -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
