On Tue, 10 Sep 2013, Matthias Kaehlcke wrote: > The old timeout value was based on the assumption that the minimum values are > used for the open and sample delay and no averaging is done. In fact the ADC > and touchscreen driver both use an open delay of 152 cycles and averaging over > 16 samples. This patch adjusts the timeout value accordingly > > Signed-off-by: Matthias Kaehlcke <[email protected]> > --- > include/linux/mfd/ti_am335x_tscadc.h | 19 ++++++++++++------- > 1 file changed, 12 insertions(+), 7 deletions(-) > > diff --git a/include/linux/mfd/ti_am335x_tscadc.h > b/include/linux/mfd/ti_am335x_tscadc.h > index db1791b..9e6a775 100644 > --- a/include/linux/mfd/ti_am335x_tscadc.h > +++ b/include/linux/mfd/ti_am335x_tscadc.h > @@ -126,13 +126,18 @@ > #define TOTAL_CHANNELS 8 > > /* > -* ADC runs at 3MHz, and it takes > -* 15 cycles to latch one data output. > -* Hence the idle time for ADC to > -* process one sample data would be > -* around 5 micro seconds. > -*/ > -#define IDLE_TIMEOUT 5 /* microsec */ > + * time in us for processing a single channel, calculated as follows: > + * > + * num cycles = open delay + (sample delay + conv time) * averaging > + * > + * num cycles: 152 + (1 + 13) * 16 = 376 > + * > + * clock frequency: 26MHz / 8 = 3.25MHz > + * clock period: 1 / 3.25MHz = 308ns > + * > + * processing time: 376 * 308ns = 116us > + */ > +#define IDLE_TIMEOUT 116 /* microsec */
Nice, clear explanation. I like it. Patch applied, thanks. -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
