Re: OMAP5912 touchscreen irq not working

Imre Deak
2006-05-28T06:02:33Z

ext David Brownell wrote:
> On Saturday 27 May 2006 1:10 pm, Imre Deak wrote:
>
>> I noticed that the ads7846 sampling rate is set too high in board-osk.c.
>> The spec allows a maximum bus frequency of 2.5MHz which gives a ~96k
>> sample rate.
>
> The spec says max sample rate of 125 KHz (at 5V) and describes Fclk
> in terms of Fsample (at an extremely fast 16 bit/sample rate) ...
> I saw no limit for Fclk, it's a function of the sample rate.

There is one table giving min/max timing values for Fclk as well and it
specifies 400ns minimum clock period. We are using the 24 bit/sample
mode (8 for command, 16 for data) which at 120kHz/sample rate would need
347ns clock period.

>
> Regardless, the max sample frequency at 3V is not 96 KHz! The
> graph shows 120 KHz... 96 KHz would be for about 2.1V.

I think, there should be a graph for each mode (15, 16, 24 bit/sample),
that one is valid for 16 bit/sample only.

>
>> There is also the uwire clock patch in my previous post,
>> which might have an effect on this issue.
>
> Unlikely; it worked before, why would it stop working suddenly?
> Including with the previous SPI clock... it's some other change
> causing the breakage.

Yes, if it worked before with the wrong clock it's probably something else.

--Imre

>
> - Dave