Hello, I configured a timer to generate a signal every 1 ms.
See below my code about the timer:
TIM_DeInit(TIMx); // TIM1 Deinitialization * TIM_InitStructure.TIM_Mode = TIM_OCM_CHANNEL_1; TIM_InitStructure.TIM_OC1_Modes = TIM_TIMING; TIM_InitStructure.TIM_Clock_Source = TIM_CLK_APB; TIM_InitStructure.TIM_Clock_Edge = TIM_CLK_EDGE_FALLING; TIM_InitStructure.TIM_Prescaler = 0xEF; // period = 5us TIM_InitStructure.TIM_Pulse_Length_1 = 0xC8; // cycle of 200 period => cycle = 1ms TIM_Init (TIMx, &TIM_InitStructure);
And the statements inside timer's interrupt:
void TIM1_IRQHandler(void) { // port 3 pin 7 activated P37_1; // ACK interrupt TIM_ClearFlag(TIM1, TIM_FLAG_OC1); // clear Output Compare 1 flag TIM_CounterCmd(TIM1, TIM_CLEAR); // Reset TIM1 Counter VIC0->VAR = 0xFF; // write any value to VIC0 VAR }
BUT my oscilloscope measured a period of 1.03 ms instead of the 1ms expected. Normally to generate a pulse every 1.03 ms the TIM_Pulse_Length_1 should be set to 0xCE. As you can see, the difference between 0xCE and 0xC8 is big.
What can be the cause of this timer's inaccuracy ? > Problem in PLL configuration ? > Problem of crystal ? > Problem in timer configuration ?
Has someone the same problem ? In advance, thank you