Question about the period of timer.

[minjiexm]

hi, Dear expert:
I am trying to use timer interrupt.
So first I need to set the timer period.
There are two functions for this purpose.
int or1k_timer_init (unsigned int hz) 
void or1k_timer_set_period (uint32_t hz)
My question is why this function does not need the input of clock cycles?
if my clock freq is 100Mhz, I think the value should different to clock freq 50Hz.

Thanks.

[jeremybennett]

I suggest this question is best asked on the LibreCores OpenRISC mailing list. Details here:

https://lists.librecores.org/

Marking as closed here.

[wallento]

Hi,

I think I can answer it here, as it directly relates to newlib and I can directly point to the code.

The period of the timer is actually Hz as you describe and it is hence platform-independent on a C level. Anyhow, as you describe correctly the actually value written to the hardware timer depends on the clock.

This happens here: https://github.com/openrisc/newlib/blob/or1k/libgloss/or1k/timer.c#L58

So, the magic value you are asking for is _or1k_board_clk_freq.

It is set for each board in its board support files: https://github.com/openrisc/newlib/tree/or1k/libgloss/or1k/boards

The board is selected with the -mboard=<board> switch.

You have two options now:

• Write your own board file based on tmpl.c, or
• Use the default board file (I think its or1ksim in GCC) and overwrite this specific value in your own software. The _or1k_board_clk_freq symbol is defined as weak, so GCC will pick your own definition.

I would prefer the second one, as long as there is nothing else you may get from writing your own board support file.

So, just define your frequency in your software:

uint32_t _or1k_board_clk_freq = <yourfreqinhz>

I hope this helps.

Cheers,
Stefan

[minjiexm]

hi， Wallento：
That is exactly what I want!
Thanks a lot.