On Thursday 12 March 2009, Eric Miao wrote: > > > > This should be a workaround for broken hardware and I don't expect > > this sync time on every boards. > > > > The sync time depends on the moment of this sync between two HSYNC, > I don't expect that to be very long, But how long is that? 1/(50 KHz) or so? > yet the hardware is broken enough to > endure this latency. Actually I heard from someone else this morning that it's not just "broken" hardware that sees touchscreen ADC sampling noise related to hsync. So this patch makes sense ... although there's no way to guarantee the SPI requests won't have queueing delays before they arrive at the touchscreen controller, possibly hitting the next hsync interval. It seems that it's surprisingly tricky to get clean samples from touchscreens. There's physical oscillation to compensate, which changes capacitance until it damps down. There's also electrical oscillation from charging the various sense lines. Add to that a bunch of honest-to-goodness noise associated with hsync and vsync... yeech! It would be a Good Thing if someone were to split out the sample filtering logic from this driver so it could be used with other touchscreen drivers. - Dave -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
