Timer 3, Interrupt frequency>1MHz

[lucas239955_st]

Posted on January 11, 2012 at 23:54

How to get interrupt frequency bigger than 1MHz ?

I have Discovery F4 Board and use Timer 3 as TIM_TimeBase Example. I have code as follow: __IO uint16_t CCR1_Val = 10000; __IO uint16_t CCR2_Val = 1000; __IO uint16_t CCR3_Val = 100; __IO uint16_t CCR4_Val = 10; PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 84000000) - 1;   TIM_TimeBaseStructure.TIM_Period = 65535;   TIM_TimeBaseStructure.TIM_Prescaler = 0;   TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;   TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;   TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);   TIM_PrescalerConfig(TIM3, PrescalerValue, TIM_PSCReloadMode_Immediate) Chanels and stm32f4xx_it.c are configured as TIM_TimeBase Example. (Measured toggling frequency)=(Interrupt frequency)/2

   TIM3CC=84MHz  

  CCRx_VAL

 Measured toggilng f. [Hz] Theoretic Interrupt f.  [Hz]

 1  10000  4200  8400

 2  1000  42000  84000

 3  100  

640.6 bad

 840000

 4  10  

406.8 bad

 8400000 Why there are bad values? Next example:

 TIM3CC=1MHz

  CCRx_VAL   Measured toggilng f. [Hz]

 Theoretic Interrupt f. [Hz]

 1  65530  7,62  15,260

 2  64000  7,81  15,625

 3  10  50000  100000

 4  5  

15,25 bad

 200000 I need  10MHz interrupt frequency in my project, how can I get this? #stm32-timer3

[Tesla DeLorean]

Posted on January 12, 2012 at 00:48

I need  10MHz interrupt frequency in my project, how can I get this?

You must be pretty new at this. Those kind of frequencies require hardware. For a processor running at 120 MHz, you'd have 12 cycles to play with at 10 MHz. The Cortex-M3 takes 12-cycles to stack an interrupt, I doubt the M4 is any better. So when do you expect to do anything? With insufficient cycles the processor will saturate and miss interrupts. Access to a peripheral device is the order of 4-cycles. At 1 MHz you'll have 120 cycles, that's a pretty tight budget to do anything practical. The timers can generate very high rates, these are designed for output pins, acting autonomously, not to be serviced by interrupts.