Question
create a frequency, use CC1 as overflow
Posted on February 16, 2012 at 16:18
I hope someon can help me.. thank you.
Hello, I want to create flanks with an Timer4 interrupt. I works if i use the interrupts from
external flanks. Now I want to create the flanks with an internal frequency. Its a little complicated to describe all so I only describe the problem. Timer 4 CC3 and CC4 are used to create the outputsignal-flanks with an interrupt. For a new flank I have to load a new value in the CC3 or CC4. But if i have a frequency wich is less than 2^16/72MHz => 918µs... I need a counter for the overflows. The counter is set to with the number of overflows and counts down with ever CC1-flag. Every time if I load the interrupt CCs i also load the CC1 with the same value. Now I can check with the CC1 flag if the timer pass the 918µs after the last flank. But if the new CC1 is to close the old CC1 one CC1-flag is left. I tryed to correct this by checking the distance beween old CC1 and new CC1 and if the distance is to low (less than 25000) I add 2^15 to the value of CC1. Oncurrent I decrease the overflowcounter because now it has to run on time more. Now it seems that the overflow is one to less if the distance is more than 19000. So I get 1 Flag to much. If the distance is more than 5000 the outputsignal is correct. Is there a better way to do this or what is the bug in the program?//new frequency
if
(Test_lock == RESET)//if new flag is ready
{ n_Tim4_exte_CC1 = (n_Frequency >>16
) +1
;//timerextension CC1
//if CC1 is set with + 2^15
if
(test_CC1 ==1
) { n_Tim4_exte_CC1--; test_CC1 =0
; TIM_ClearFlag(TIM4, TIM_FLAG_CC1); } Test_lock = SET;//lock this function
}//32 bit extension
if
(TIM_GetFlagStatus(TIM4, TIM_FLAG_CC1) == SET &&//if timer pass CC1
n_Tim4_exte_CC1 >0
)//if not all overflow completed
{ n_Tim4_exte_CC1 --; TIM_ClearFlag(TIM4, TIM_FLAG_CC1); }//free for next outputflank
if
(n_Tim4_exte_CC1 ==0
&&//extension is 0
Flag_pos_Flank_dumped== SET &&//last flanks finshed
Flag_neg_Flank_dumped== SET ) { Flag_High_Flank = SET;//function to set the new interrupts can be used 1 time
n_Timer4_output_start_pos = (n_Timer4_Impulsestart + n_Frequency);//new outputflank value
Test_lock = RESET;//enable first if-function again
//if the new CC1 is to close the the old CC1
if
((n_Timer4_output_start_pos > n_Timer4_Impulsestart && (n_Timer4_output_start_pos - n_Timer4_Impulsestart) <25000
) || (n_Timer4_output_start_pos < n_Timer4_Impulsestart && (65535
- n_Timer4_Impulsestart + n_Timer4_output_start_pos) <25000
)) { TIM_SetCompare1(TIM4, (n_Timer4_output_start_pos +32767
));//set CC1 opposite
test_CC1 =1
; TIM_ClearFlag(TIM4, TIM_FLAG_CC1); }else
{ TIM_SetCompare1(TIM4, n_Timer4_output_start_pos);//set CC1 at the same value like the new flank
} } I hope someon can help me.. thank you. 