A while ago I received an STM32 discoveryboard as a gift, after I told some people on a fair that I'm a software engineer. Because I'm allready experienced in C/C++ but new to embedded software engineering, I ordered a course. Now I get stuck on the chapter on Timers, because the software I wrote just isn't working as it should. Here's my source file, I'm working with Atollic Truestudio.
#include "stm32f7xx.h"
int period;
float freq;
int main(void)
{
int last_value = 0;
int current_value = 0;
RCC->AHB1ENR |= 0x109; // GPIOA for PA5 blue led, GPIOD for TIM4, GPIOI for TIM5
GPIOD->MODER |= 0x2000000; // Select alternate function for PD12
GPIOD->AFR[1] |= 0x20000; // Alternate function 2 (TIM4_CH1) for PD12
RCC->APB1ENR |= 0x4; // Enable clock for TIM4
// This sets up a 1Hz Timer, TIM4_CH1 in output compare mode
TIM4->PSC = 1600-1; // Set the value for the prescaler
TIM4->ARR = 10000-1; // Set the value for the autoreloadregister
// Set the output to toggle on match
TIM4->CCMR1 |= 0x30; // Set the output to toggle on match
TIM4->CCR1 |= 0x0; // Set the match value
TIM4->CCER |= 0x1; // Set OC1 signal as output on PD12
TIM4->CNT = 0x0;
TIM4->CR1 = 0x1; // Counter Enable
// This sets up TIM5_CH4 in input capture mode
GPIOI->MODER |= 0x2; // Set alternate function for PI0
GPIOI->AFR[0] |= 0x2; // Alternate function 2 (TIM5_CH4) for PI0
RCC->APB1ENR |= 0x8; // Enable clock for TIM5
TIM5->PSC |= 16000-1;
TIM5->CCMR2 |= 0x4100; // Channel 4 is input, sampling every 6 ocurrences
TIM5->CCER |= 0xB000; // Enable capture, Capture rising and falling edge
TIM5->CR1 |= 0x1; // Counter enable
while (1)
{
while(!(TIM5->SR & 0x10)){} // Wait until edge is captured. HERE PROGRAM FLOW GETS STUCK
// The part below this comment never gets executed,
// except when I disconnect and reconnect the jumper wire between PD12 and PI0,
// then the while loop condition gets matched once.
current_value = TIM5->CCR4;
period = current_value - last_value;
last_value = current_value;
freq = 1000.0f / period;
}
}
According to what I learned from the course and what I found in the reference manual, https://www.st.com/content/ccc/resource/technical/document/reference_manual/group0/c8/6b/6e/ce/dd/f7/4b/97/DM00305990/files/DM00305990.pdf/jcr:content/translations/en.DM00305990.pdf , this should work.
However, I noticed something remarkable in the manual. In chapter '19.4.7 TIMx capture/compare mode register 1 (TIMx_CCMR1)(x = 2 to 5)', 'Bits 6:4 OC1M: Output compare 1 mode.'
OC1M is a three bit field in the register diagram, however the options provided in this chapter for setting up this register all consist out of four bits. This doesn't make sense to me. Anyways, following the instructions from chapter '19.3.8 Output compare mode' I set OC1M to '011' to toggle on match.
If I understood everything right, this should set the output on PD12 to high when it's low and to low when it's high, when the value in CNT matches the value in CR1. This should be the signal that goes trough the jumper wire and should get captured by TIM5 that I assume to be running in input capture mode.
I suppose that TIM5 indeed is capturing input, due to the fact that the while loop condition that I have marked in the source file's comments gets matched when I unplug and then replug the jumperwire.
I also have a different version of this program, where I commented out the part on setting up and enabling TIM4 and decided to use plain GPIO output from PD12, by setting up GPIOD in General purpose output mode and replacing the while (1) statement with the following code.
GPIOD->MODER = 0x100000;
GPIOD->ODR = 0;
while (1)
{
while(!(TIM5->SR & 0x10))
{
//GPIOI->BSRR = (GPIOI->BSRR & 0x1) ? 0x10000 : 0x1;
if(GPIOD->ODR&0x1000)
{
GPIOD->ODR=0;
}
else
{
GPIOD->ODR=0x1000;
}
delayMs(25);
} // Wait until edge is captured
current_value = TIM5->CCR4;
period = current_value - last_value;
last_value = current_value;
freq = 1000.0f / period;
}
If I'm right this should work more or less the same as the blinking led example that I got to work earlier in the same course, but now on the timer input.
I would appreciate it if anyone with more experience than me or with better equipment available as I got could take a closer look on this issue.
Thanks in advance, Ronnie van Aarle.
