Skip to main content
StephanMair
StephanMair
Associate III
September 19, 2020
Question

TIM2 fires off interrupt at the same interval despite drastically different prescaler and period values

  • September 19, 2020
  • 2 replies
  • 1429 views

Hi:

My platform: STM32WB55CE.

I'm using internal clock.

I have rigged the TIM2 with an interrupt function. The interrupt could fire, but it will be fired right after all the initialization were done. More over, no matter how I change the prescaler value or the period value for TIM2's init struct, the interrupt seems always fire at the same short, <1second interval.

I don't know where to begin, this is quite strange! Did I configured the wrong clock source? I heard that if you designated the wrong clock source the timer shouldn't work at all.

Please help!

This topic has been closed for replies.

2 replies

TDK
TDK
Super User
September 19, 2020

Are you adjusting the registers or just the initialization structure?

"If you feel a post has answered your question, please click ""Accept as Solution""."
StephanMair
StephanMairAuthor
Associate III
September 20, 2020

Hi: Thank you for your reply!

Only the init struct.

But please understand that by "time hasn't changed" I mean it hasn't changed even after I reset the chip and ran from the very start. I understand that you need to adjust the registers in real time for it to take effect in real time. In my case I don't need real time changes.

Unless even for the first time, you need to do a run-time change on the register for everything to work, that would be nuts!

Could it be I'm overflowing the prescaler and period related registers? For prescaler I'm using value 9999, and period I'm also using 9999. I've tried to increase it to 999,999 each in order to observe changes, but nothing.

TDK
TDK
Super User
September 20, 2020
You're probably just not running the code you think you're running. There's unlikely to be a major fault in the hardware where the prescaler/auto-reload registers are ignored.
Examine the register values while running to ensure they're updated and behaving correctly.
Note that 999,999 is not a 16-bit value so isn't going to work for 16-bit registers.
How are you verifying the interrupt frequency is incorrect?
"If you feel a post has answered your question, please click ""Accept as Solution""."
TDK
TDK
Super User
September 20, 2020

> Unlikely... or the ISR shouldn't fire.

You don't think incorrect code could also trigger the ISR?

> See here's the problem

You can adjust the prescaler, reload counter and clock divider. You could also set the interval to smaller than you want and have a counter variable which increments and only takes action when appropriate. There are also 32-bit timers (TIM2) which accept a 32-bit ARR value (but still only a 16-bit PSC). You could also set the system clock to 4MHz if that's what you really want. Lots of solutions here.

Edit:

If you want a timer to update at 0.2 Hz, this is possible even at max clock speed and without using the clock divider:

32MHz / 65536 / 65536 = 0.00745 Hz

"If you feel a post has answered your question, please click ""Accept as Solution""."
StephanMair
StephanMairAuthor
Associate III
September 26, 2020

Hi TDK! Thank you for your replies!

Sorry to bother you again but you are right! My code isn't working... so

>You don't think incorrect code could also trigger the ISR?

I sure do now lol

Anyway here's my HAL code:

static void MX_TIM2_Init(void)
 
{
 
 
 /* USER CODE BEGIN TIM2_Init 0 */
 
 
 /* USER CODE END TIM2_Init 0 */
 
 
 TIM_ClockConfigTypeDef sClockSourceConfig = {0};
 
 TIM_MasterConfigTypeDef sMasterConfig = {0};
 
 
 /* USER CODE BEGIN TIM2_Init 1 */
 
 
 /* USER CODE END TIM2_Init 1 */
 
 htim2.Instance = TIM2;
 
 htim2.Init.Prescaler = 16000;
 
 htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
 
 htim2.Init.Period = 16000;
 
 htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
 
 htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
 
 if (HAL_TIM_Base_Init(&htim2) != HAL_OK)
 
 {
 
 Error_Handler();
 
 }
 
 sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
 
 if (HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig) != HAL_OK)
 
 {
 
 Error_Handler();
 
 }
 
 sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
 
 sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
 
 if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
 
 {
 
 Error_Handler();
 
 }
 
 
 if (HAL_TIM_RegisterCallback(&htim2,HAL_TIM_PERIOD_ELAPSED_CB_ID,TIM2_Cb) != HAL_OK)
 
 {
 
 Error_Handler();
 
 }
 
 
 /* USER CODE BEGIN TIM2_Init 2 */
 
 
 /* USER CODE END TIM2_Init 2 */
 
 
}
 
 
 
 if (HAL_TIM_Base_Start_IT(&htim2) != HAL_OK)
 
 {
 
 /* Starting Error */
 
 Error_Handler();
 
 }
 
 

And here's the screen cap of my registers, obviously not right...

0693W000004HCGpQAO.png

I put the breakpoint after all the initialization were done. What went wrong? Some of the registers have the right value, most don't.

Please help... once more!

Terms & ConditionsAccessibility statement