[U-Boot-Users] [PATCH 04/10 v2] [ARM] TQMA31: add new board with i.MX31 processor

[Sascha Hauer]

Hi,

On Tue, Jul 08, 2008 at 05:14:35PM +0200, Jens Gehrlein wrote:
> Wolfgang Denk schrieb:
>> In message <20080708093022.9272.4677.stgit at tq-sewsrv-4.tq-net.de> you wrote:
>>> +/* Timer tick */
>>> +#define CFG_HZ				32768
>>
>> CFG_HZ is a constant and has to be 1000.

Why is it a board specific define then?

>
> I know, we had a discussion earlier about that issue (see "i.MX31:  
> question about CFG_HZ and CKIL" of 7th May). The situation is as follows:
>
> The TQMA31, as well as the mx32ads use the General Purpose Timer 1,  
> which is feeded by a 32768 clock (possibly imx31_litekit and  
> imx31_phycore with 32000 Hz? I don't know.). The prescale divider can  
> only be an integer. 32768/1000 = non-integer.
>
> The counter is just read. There are no real interrupts (I mention it,  
> because you wrote about this earlier).
> The origin source code is from U-Boot V2, I suppose. Guennadi used it  
> for the mx31ads.

Not quite correct, I wrote the original mx31 code for U-Boot V1 and then
ported it to V2. I think Guennadis work is based on the V1 work.

>
> Currently, I see only one way to solve this:
> 1. Patch the common file cpu/arm1136/mx31/interrupts.c, function  
> interrupt_init(), so that the prescaler divides by 33.
> Alternatively, also make the divider a board specific define.
> 2. Patch all mx31 board config header files with CFG_HZ 1000.
> 3. All mx31 boards have to be tested.
>
> The following is impossible:
> - changing the HW
> - using an internal clock, because maximum is 1000 Hz * 4096 = 4096000  
> Hz (the maximum divider is 4096). All internal clocks are much higher.
> Please for correction if I'm wrong.

You could add a software divider in get_timer(). But I think it's better
to define CFG_HZ to whatever the timer frequency is. At least 49 boards
do it.

Regards
  Sascha

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