Clock Function in not called in the expected period

Hi Tim,

Do you know at what frequency your CPU clock is running? If it's running at a speed different from what BIOS thinks it's running at, it could account for the differences you're seeing.

Once you find out how many Hz it's actually running at, you can tell BIOS in your cfg script by setting BIOS.cpuFreq.lo to that value.

Whitney

I didn't make any changes to the Cpu clock frequency. Its 550 MHz - thats the initial value of the SYS/BIOS example programms .

I guess if the CPU clock was wrong the difference between expected period and real period of the swi-clock-funktion would be bigger?!

Tim,

I think the timer peripheral used by the Clock module must be configured for 32768Hz for your application, and this is limiting the resolution you can get for the Clock ticks.

If the timer is running at 32768Hz, then 100usec is 3.2768 ticks.  Rounding downwards, this is 3 timer counts, and 3/32768 =  91.5usec.  Similarly, 500usec is 16.384 ticks, rounding down is 16 ticks, so 16/32768 = 488.2usec.  But for 1000usec I would have expected something like 977usec, versus the 1005usec you report, not sure why that one is different.

Anyways, please see this thread about Clock and the tick rate resolution on an AM3359, and how to change it: http://e2e.ti.com/support/embedded/bios/f/355/p/267580/937908.aspx#937908

Scott

Hi Scott,

thank you for the answer.

What you wrote makes sense to me. With (33 ticks) / (32768 ticks per s) = 1007 us that fits for the last value too.

At the moment I'm using a Timer (24 MHz clocked) with a HWI to post the SWIs. This works fine, also for shorter periods.

Void main()
{
    Timer_Handle hdl_timer = 0;
    Timer_Params timerParams;
    Error_Block eb;

    mmuInit(applMmuEntries);

    Error_init(&eb);

    DMTimer3ModuleClkConfig();           //enable Clock for DMTimer 3

    Timer_Params_init(&timerParams);

    timerParams.extFreq.lo = 24000000;   //Timer Frequency
    timerParams.extFreq.hi = 0;
    timerParams.period = 63;             //Period 63 us
    timerParams.periodType = Timer_PeriodType_MICROSECS;
    timerParams.arg = 1;

    hdl_timer = Timer_create(1, (ti_sysbios_interfaces_ITimer_FuncPtr)Timer0Func, &timerParams, &eb);  // 1 stands for DMTimer3

    [...]
    BIOS_start();     /* enable interrupts and start SYS/BIOS */

}

I'll try to change the timer for the Clock Module later to get the perviously desired Clock/SWI solution without using HWIs. I'll report if it worked...

Regards,

Tim

Scott Gary said:

Anyways, please see this thread about Clock and the tick rate resolution on an AM3359, and how to change it: http://e2e.ti.com/support/embedded/bios/f/355/p/267580/937908.aspx#937908

To get a 24 MHz based Clock Tick I tried to use to use DMTimer4. After reading through the topic in your link I changed the connect-function of my GEL file to:

OnTargetConnect()
{
    unsigned int i;
    GEL_MapOff();
    GEL_MapReset();
    GEL_MapAddStr(0x00020000, 0, 0x0000C000, "R", 0);    // Boot ROM
    [...]
    GEL_MapAddStr(0x80000000, 0, 0x10000000, "R|W", 0);  // 256MB DDR2 external memory
    GEL_MapOn();
    GEL_Reset();             //reset the board to avoid conflicts with program running from NAND
    for(i=0;i<100000;i++);
    AM335xStartState();
    AM3359_ICE_Initialization();

    WR_MEM_32(CM_PER_TIMER4_CLKCTRL, 0x2);      //Enable Timer4
    WR_MEM_32(CLKSEL_TIMER4_CLK, 0x1);          //Clock source CLK_M_OSC (24 MHz)
    GEL_TextOut("Timer4 init done\n");

    Disable_Watchdog();
}

In the cfg script I changed timerID of the Clock Module from ANY to 2 (for DMTimer4). The important lines are:

Clock.tickPeriod = 100;
Clock.timerId = 2;
[...]
var clock0Params = new Clock.Params();
clock0Params.instance.name = "clock0";
clock0Params.period = 1;
clock0Params.startFlag = true;
Program.global.clock0 = Clock.create("&clk0Func", 200, clock0Params);
Clock.tickMode = Clock.TickMode_PERIODIC;

Theres no change in the behavior. Still the measured clock periods aren't right. Adding the following lines the the config code ends up in the same error as in the link you posted, although i changed the GEL file.

var Timer = xdc.useModule('ti.sysbios.timers.dmtimer.Timer');
Timer.intFreq.hi = 0;
Timer.intFreq.lo = 20000000;

What is the trick to get the Clock module tick in multiples of a 24 MHz Timer?

Scott,

it seems to work now. On friday I still meassured the wrong times although i changed the Timer settings... I can't reproduce that now so it probably was my fault.

To put it all together:

Added to the GEL File:
#define CM_DPLL (0x44e00500)
#define CM_PER_TIMER4_CLKCTRL (PRCM_BASE_ADDR + 0x88)
#define CLKSEL_TIMER4_CLK (CM_DPLL + 0x10)
[...]
         //Following Lines in the Connect Function
    WR_MEM_32(CM_PER_TIMER4_CLKCTRL, 0x2);      //Enable DMTimer4
    WR_MEM_32(CLKSEL_TIMER4_CLK, 0x1);          //Clk Source: CLK_M_OSC

Changed / Added in the cfg file:
var Timer = xdc.useModule('ti.sysbios.timers.dmtimer.Timer');
Timer.intFreq.hi = 0;
Timer.intFreq.lo = 24000000;
[...]
Clock.timerId = 2;   //DMTimer4

Regards,

Tim