AN3140

3-read software workaround

Doc ID 16997 Rev 1

9/14

5

3-read software workaround

Below you can see a proposal for a software workaround that works for the scenario

described in the previous section. This workaround works well in case of the previously

described scenario, where READ_Clk is much faster than CNT_Clk, as well as when they

have similar frequencies.

In the first case the MAX_DIFF should be defined as ‘1’, while in the second case (similar

frequencies) a higher value should be selected. This value should be fine tuned depending

to the two real frequencies.

Example code

/*

* The following routine implents the 3-read workaround.

* MAX_DIFF equals to 5 should work in case of READ_Clk==75MHz and

* CNT_Clk==48MHz.

*/

#define MAX_DIFF 5

bool Timer_Read_Workaround(UINT32 *valid_timer_cnt_value)

{

UINT32 timer_value1, timer_value2, timer_value3;

UINT32 valid_timer_cnt_value;

/* To avoid any interrupt that might delay the reading. */

DISABLE_ALL_INTERRUPT;

timer_value1 =

READ_TIMER_CNT();

timer_value2 =

READ_TIMER_CNT();

timer_value3 =

READ_TIMER_CNT();

ENABLE_ALL_INTERRUPT;

if ((timer_value2 – timer_value1) <= MAX_DIFF) {

*valid_timer_cnt_value = timer_value2;

}

else if ((timer_value3 – timer_value1) <= MAX_DIFF) {

*valid_timer_cnt_value = timer_value3;

}

else if ((timer_value3 – timer_value2) <= MAX_DIFF) {

*valid_timer_cnt_value = timer_value2;

}

else

return FALSE;

return TRUE;

}