On Tuesday 12 November 2013 2:10:38 pm Priscilla Wong wrote: > On 12/11/13 04:01 PM, Steven King wrote: > > On Tuesday 12 November 2013 11:15:07 am Priscilla Wong wrote: > >> Can someone help me on an issue I am seeing on my i2c-imx driver for > >> uClinux 2.6.29? > >> > >> Attached is a scope capture of an i2c read operation. In the capture, > >> yellow is clock, green is data, blue and pink are both gpios I am using > >> for debugging. It can be seen that there is a 300 us delay after master > >> writes to the slave address. The transfer is complete when the interrupt > >> arrives and waitqueue is woken up. The pink gpio fires high during the > >> transfer complete call (i2c_imx_trx_complete) after the slave address is > >> written. The blue gpio fires high during the queue wake up call in the > >> ISR (i2c_imx_isr). When looking at this capture, my first inclination is > >> to bump the interrupt level and priority, hoping it will speed up the > >> ISR but it had no effect on the delay. > >> > >> Any ideas what is causing this delay? > > > > That looks similar to an issue with the original version of my > > i2c-coldfire driver; the scheduler simply can't reschedule tasks any > > faster than that. The fix was to have the isr process the next byte in > > the transfer and only send the completion when the entire message was > > transfered. > > Thanks for your input! > > Would changing the implementation to polling based be the answer given > that i2c-mcf did not have this issue? I've attached a scope image of a > read access with i2c-mcf (i2c-mcf-i2cget.png). However if switching > i2c-imx to polling based, the data transferring bit (ICF) also suffers > from this delay too. It is not set till 228us after the 9th clock cycle > (See attached scope15.png image, cursor X1 is the 9th clock cycle and X2 > is when ICF is set). Any ideas?
Sorry, I'm not familiar with those drivers but I would guess its something similar, a context switch or superfluous udelay somewher. _______________________________________________ uClinux-dev mailing list uClinux-dev@uclinux.org http://mailman.uclinux.org/mailman/listinfo/uclinux-dev This message was resent by uclinux-dev@uclinux.org To unsubscribe see: http://mailman.uclinux.org/mailman/options/uclinux-dev
