Changing PWM parameters in the middle of operation causes incorrect timing behavior?
Good day everybody,
In my current application (IR signal generation) I need to change the PWM width for every bit that I want to send. In my implementation (seen below) I change the ARR and CCR1 values for the durations that I need, and then I generate an update event with TIM16->EGR |= TIM_EGR_UG; to reset the timer, and then I start it in PWM mode with the HAL_TIM_PWM_Start() function.
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
if(htim->Instance == TIM16)
{
toggleflag = 1;
}
}
void Send_PowerNEC(uint32_t code)
{
// 1. header for the IR: 4.5ms chirp, 4.5ms 0
TIM16->CCR1 = 36000;
TIM16->ARR = 54000;
TIM16->CNT = 0;
TIM16->EGR |= TIM_EGR_UG;
__HAL_TIM_ENABLE_IT(&htim16, TIM_IT_UPDATE);
HAL_TIM_PWM_Start(&htim16, TIM_CHANNEL_1);
toggleflag = 0;
while(toggleflag == 0);
toggleflag = 0;
HAL_TIM_PWM_Stop(&htim16, TIM_CHANNEL_1);
TIM16->EGR |= TIM_EGR_UG;
// 2. sending the string
uint32_t tosend = 0x0045FF00;
for(int i=0; i<32; i++)
{
if(tosend & 1)
{
TIM16->CCR1 = 2240;
TIM16->ARR = 9000-1;
TIM16->CNT = 0;
__HAL_TIM_ENABLE_IT(&htim16, TIM_IT_UPDATE);
TIM16->EGR |= TIM_EGR_UG;
HAL_TIM_PWM_Start(&htim16, TIM_CHANNEL_1);
toggleflag = 0;
while(toggleflag == 0);
toggleflag = 0;
}
else
{
TIM16->CCR1 = 2240;
TIM16->ARR = 4500-1;
TIM16->CNT = 0;
__HAL_TIM_ENABLE_IT(&htim16, TIM_IT_UPDATE);
TIM16->EGR |= TIM_EGR_UG;
toggleflag = 0;
while(toggleflag == 0);
toggleflag = 0;
}
HAL_TIM_PWM_Stop(&htim16, TIM_CHANNEL_1);
TIM16->EGR |= TIM_EGR_UG;
tosend >>= 1;
}
}The timer clock is set to 8MHz and the prescaler is 1, and PWM is set to mode 2, so for the first signal (ARR=54000, CCR1=36000) I must get a 1 for 9ms and a 0 for 4.5ms, and I indeed get the correct output on the MCU pin. However sadly here is where the accuracy ends.
From then on, if the LSB bit is 1 I set ARR=9000 and CCR1=2240, and if the LSB bit is zero I set ARR=4500 and CCR1=2240. So theoretically I must get 560us of 1 in both cases and 1.68ms and 560us of 0 on the pin. However after observing the PWM output pin with a logic analyzer, I get this:
which means that the output timings are incorrect.
What can cause this problem? The PWM output pin only works correctly the first time and when I change the CCR1 and ARR values and generate an update event afterwards, I get incorrect results.
Thanks for your time. Also here is my timer configuration:
static void MX_TIM16_Init(void)
{
/* USER CODE BEGIN TIM16_Init 0 */
/* USER CODE END TIM16_Init 0 */
TIM_OC_InitTypeDef sConfigOC = {0};
TIM_BreakDeadTimeConfigTypeDef sBreakDeadTimeConfig = {0};
/* USER CODE BEGIN TIM16_Init 1 */
/* USER CODE END TIM16_Init 1 */
htim16.Instance = TIM16;
htim16.Init.Prescaler = 1;
htim16.Init.CounterMode = TIM_COUNTERMODE_UP;
htim16.Init.Period = 18000-1;
htim16.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
htim16.Init.RepetitionCounter = 0;
htim16.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
if (HAL_TIM_Base_Init(&htim16) != HAL_OK)
{
Error_Handler();
}
if (HAL_TIM_PWM_Init(&htim16) != HAL_OK)
{
Error_Handler();
}
sConfigOC.OCMode = TIM_OCMODE_PWM1;
sConfigOC.Pulse = 0;
sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
sConfigOC.OCNPolarity = TIM_OCNPOLARITY_HIGH;
sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
sConfigOC.OCIdleState = TIM_OCIDLESTATE_RESET;
sConfigOC.OCNIdleState = TIM_OCNIDLESTATE_RESET;
if (HAL_TIM_PWM_ConfigChannel(&htim16, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
{
Error_Handler();
}
sBreakDeadTimeConfig.OffStateRunMode = TIM_OSSR_DISABLE;
sBreakDeadTimeConfig.OffStateIDLEMode = TIM_OSSI_DISABLE;
sBreakDeadTimeConfig.LockLevel = TIM_LOCKLEVEL_OFF;
sBreakDeadTimeConfig.DeadTime = 0;
sBreakDeadTimeConfig.BreakState = TIM_BREAK_DISABLE;
sBreakDeadTimeConfig.BreakPolarity = TIM_BREAKPOLARITY_HIGH;
sBreakDeadTimeConfig.BreakFilter = 0;
sBreakDeadTimeConfig.AutomaticOutput = TIM_AUTOMATICOUTPUT_DISABLE;
if (HAL_TIMEx_ConfigBreakDeadTime(&htim16, &sBreakDeadTimeConfig) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN TIM16_Init 2 */
/* USER CODE END TIM16_Init 2 */
HAL_TIM_MspPostInit(&htim16);
}