* Ladislav Michl <ladis@xxxxxxxxxxxxxx> [171109 21:49]: > gpio_in (yellow) is fed with signal generator while scope inputs are > connected to both gpio_in and gpio_out (blue). Output signal is inverted > to make waveform compare easier by naked eye. > > Expected result is clean waveform with small offset and reasonable jitter. > To make this clearly visible, waveform persistence was enabled on scope. > Resulting waveform on idle system looks like this: > http://ladislav.michl.sweb.cz/omap3_edge_irq_1.png > As you can see, latency (jitter) is up to half of pulse width, which seems > pretty bad as frequency is 610Hz. Nice test set up :) > However, loaded system (*) shows much better results: > http://ladislav.michl.sweb.cz/omap3_edge_irq_2.png > > Any idea how to get good enough (second measurement) results regardless of > the system load? Maybe you can block idle states from your driver with PM QoS? Just add some latency requirement. See for example what was done earlier for omap3 audio in commit 9834ffd1ecc3 ("ASoC: omap-mcbsp: Add PM QoS support for McBSP to prevent glitches"). Not sure if we can do this in a generic way.. But maybe it's doable for things like PWM drivers. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
