Calculation of the interruption time of Timer ( SYS / BIOS ) - C6748

Rafael,

Now that I see your screenshot, I'm not sure if my answer below is what you are looking for, but it may help explain some observations.

The TIMER modules have different reference clock sources on this device, hence the clocking diagram.  TIMERs 0 and 1 both use AUXCLK (device input clock) as the reference frequency, whereas TIMERs 2 and 3 can be configured to use PLL0/2 or PLL1/2 as the reference frequency.

Since you have TIMER1 pulled up in the picture, we can use that as the example.  If the device has a 24MHz input clock and you want an interrupt at 500us, the number of cycles would be 24MHz x 500us = 12,000 TIMER cycles.

If you are observing something different, it may be because 1) BIOS is configuring TIMER in a manner which is different from what we expect and we can verify that by reading the TIMER registers, or 2) the simulator may be configured differently.

-Tommy

Rafael --

The simulator timer runs at 50MHz.  You can change the simulator .cfg file to be 25MHz.  Unfortunately, the simulator's clock input frequency can only be a divisor of the CPU frequency.

From C:\Program Files\Texas Instruments\ccsv5.0.1.00036\ccsv5\ccs_base_5.0.1.00036\simulation\bin\configurations\tisim_c6747_ca.cfg

        // Clock divide ratio
        // The Clock freq is always fixed to be 50MHz.
        // Core is running at 300Mhz hence the divide ratio is 6
        CLOCK_DIVIDE 6;

        // Clock divide ratio
        // Uncomment this line to run the Timer at 25 MHz.
        // Core is running at 300Mhz hence the divide ratio is 12
        // CLOCK_DIVIDE 12

You should be able to change that 24000000 input frequency to 50000000 and get what you expect.

See this post for related info:

http://e2e.ti.com/support/embedded/f/355/p/96179/338489.aspx#338489

Karl and Tommy

His answers did not solve my problem, but it were fundamental.  I solved through their responses.

My simulator uses the file "tisim_c674x_ca.cfg”.  In this file has the following configuration:

/ / Clock divide ratio

CLOCK_DIVIDE 8 ;

I changed to :

CLOCK_DIVIDE 1;

Now , with the setup I described (CPU Freq = 300MHz ; Timer Period = 500 ; PeriodType = MICROSECS ) the timer interrupt is generated every 12,000 cycles , ie (1 / 24000000) * 12000 = 500us .  Exactly the expected value.

Changing the Setup to "PeriodType = Counts" I have a timer interrupt every 500 cycles.

Thank you for your help .