AT91SAM9260: How to output PCK0 clock on a GPIO pin

[Pedro I. Sanchez]

On Mon, 31 Aug 2009 12:58:30 -0400, Stephen Munnings
<smunnings at gabaedevelopment.com> wrote:
> Pedro I. Sanchez wrote:
>> Hello,
>>
>> I'm trying to get a clock on pin PC6 of my AT1SAM9260-based board and I
>> would like some advice on how to do it. For all purposes this board can
>> be
>> considered to be a clone of the sam9260ek evaluation board.
>>
>> I see doing this as a two-step process: First, link pin PC6 to the PCK0
>> clock. Second, program and enable the clock. My kernel module has the
>> following code (I'm using kernel 2.26.29.3):
>>
>> Step 1:
>>
>> at91_set_A_periph(AT91_PIN_PC6, 0);
>>
>> I'm taking this piece of code from somewhere else. is this all I need to
>> do
>> for step 1?
>>
>>
>> Step 2:
>>
>> pck0 = clk_get(NULL, "pck0");
>> if (IS_ERR(pck0)) {
>> pr_err("%s: Failed to get PCK0\n", __func__);
>> ret = PTR_ERR(pck0);
>> goto err;
>> }
>> pllb = clk_get(NULL, "pllb");
>> if (IS_ERR(pllb)) {
>> pr_err("%s: Failed to get PLLB\n", __func__);
>> ret = PTR_ERR(pllb);
>> goto err_pllb;
>> }
>> ret = clk_set_parent(pck0, pllb);
>> if (ret != 0) {
>> pr_err("%s: Failed to set PCK0 parent\n", __func__);
>> goto err_parent;
>> }
>> clk_set_rate(pck0, 11289600);
>> clk_enable(pck0);
>> clk_put(pllb);
>>
>>
>> Neither step fails. Step 2 gives me a printout "PCK0 rate 6000000Hz"
>> which
>> is not what I expected, some clock divisor must be in the way, but at
>> least
>> it is a clock of some kind. Unfortunately nothing is output on pin PC6.
>>
>> Could you provide me with some advice on how to do this properly?
>>
>> Thank you,
>>
>>   
> Here is the code I use to get PC1 to be 50Mhz (from PLLA which is 
> running at 800Mhz - this is actually on a 9G20, not a 9620)
> 
>     pck0 = clk_get(NULL, "pck0");
>     plla = clk_get(NULL, "plla");
> 
>     at91_set_B_periph(AT91_PIN_PC1, 0);    /* PCK0 */
> 
>     clk_set_parent(pck0, plla);
>     clk_set_rate(pck0, 50000000);
>     clk_enable(pck0);
> 
> There are some differences (I use PC1, not PC6; I use PLLA, not PLLB,
> etc.,)
> 
> I am not sure what the "clk_put(pllb)" does for you.  I certainly did 
> not need something like that. (PLLA was already running just fine)
> 
> But, I also found that you must have the PMC clock for the GPIOC bank 
> running before GPIO (even the configuration, it seems) will work.
> I am not sure if I had this issue in Linux, or only in the loaders, but 
> I did have to turn on the PMC clocks to get any GPIO based things
working.
> The standard boot loader only seems to turn on GPIOA, but I am also 
> using GPIOB and GPIOC, and I had to turn on the PMC clocks for those
> also before I could get very far.
> 
> Stephen Munnings

Thanks Stephen,

And how do I turn on the PMC clocks for the GPIO?

-- 
Pedro I. Sanchez