The following on DiscoF4 produces a "blinking" pulse-train on both PA11=TIM1_CH4 and PD15=TIM4_CH4 (I used PD15 first, as it's connected to the blue LED so I can see the blinking, whereas PA11 is not even brought out to the headers so I had to probe R58 using oscilloscope).
#include "stm32f4xx.h"
// #include "stm32f4xx_augment.h"
// #include "common.h"
// #include "common_gcc.h"
// blinking with blue LED through setting it as TIM4_CH4
/*
Disco F407
4LEDS on PD12..PD15, these are also TIM4_CH1..CH4
*/
#define LED_PORT GPIOD
#define LED_PIN 15
// BUTTON PA0, switches to VCC
#define BUTTON_PORT GPIOA
#define BUTTON_PIN 0
// default HSI 16MHz clock
#define CLOCK_MHZ 16
// -------- utils/frameworks
// trivial loopdelay
static void LoopDelay(volatile uint32_t n) {
while(n > 0) n--;
}
#define DELAY_CONSTANT 1000000
// ---------------------------- MAIN ------------------------------
int main(void) {
RCC->AHB1ENR |= 0
| RCC_AHB1ENR_GPIOAEN
| RCC_AHB1ENR_GPIODEN
;
RCC->APB1ENR |= 0
| RCC_APB1ENR_TIM4EN
;
RCC->APB2ENR |= 0
| RCC_APB2ENR_TIM1EN
;
// in GPIOA->MODER, PA0 is at default as Input
// and there's also an external pulldown, so no need to switch on the internal one
GPIOA->MODER = (GPIOA->MODER // assuming reset value
) | (0
| (0b10 << GPIO_MODER_MODER11_Pos) // PA11, TIM1_CH4 - OTG_FS_DM, R58
);
GPIOA->AFR[1] = GPIOA->AFR[1] | (0
| (1 << GPIO_AFRH_AFSEL11_Pos) // TIM1 is AF1
);
GPIOD->MODER = (GPIOD->MODER // assuming reset value
) | (0
| (0b10 << GPIO_MODER_MODER15_Pos) // blue LED, 0b10 = GPIO_Mode_AF
);
GPIOD->AFR[1] = GPIOD->AFR[1] | (0
| (2 << GPIO_AFRH_AFSEL15_Pos) // TIM4 is AF2
);
TIM4->CCER = 0
| TIM_CCER_CC4E // enable TIM4_CH4
;
TIM1->CCER = 0
| TIM_CCER_CC4E // enable TIM1_CH4
;
TIM1->BDTR = 0
| TIM_BDTR_MOE // enable TIM1 outputs
;
while(1) {
TIM4->CCMR2 = 0
| (0b00 << TIM_CCMR2_CC4S_Pos) // CH4 select 0b00 = output compare
| (0b101 << TIM_CCMR2_OC4M_Pos) // 0b101 = Force Active
;
TIM1->CCMR2 = 0
| (0b00 << TIM_CCMR2_CC4S_Pos) // CH4 select 0b00 = output compare
| (0b101 << TIM_CCMR2_OC4M_Pos) // 0b101 = Force Active
;
LoopDelay(DELAY_CONSTANT);
if (BUTTON_PORT->IDR & (1 << BUTTON_PIN)) {
LoopDelay(3 * DELAY_CONSTANT);
}
TIM4->CCMR2 = 0
| (0b00 << TIM_CCMR2_CC4S_Pos) // CH4 select 0b00 = output compare
| (0b100 << TIM_CCMR2_OC4M_Pos) // 0b100 = Force Inactive
;
TIM1->CCMR2 = 0
| (0b00 << TIM_CCMR2_CC4S_Pos) // CH4 select 0b00 = output compare
| (0b100 << TIM_CCMR2_OC4M_Pos) // 0b100 = Force Inactive
;
LoopDelay(DELAY_CONSTANT);
}
}
As far as TIM1 is concerned:
In RCC, I enable clock for GPIOA and TIM1.
In GPIOA, I set MODER for pin PA11 to 0b10 = AF, and AFR[1] to 1 (TIM1=AF1).
In TIM1, I set
- CCER.CC4E = 1
- BDTR.MOE = 1
- CCMR2.CC4S = 0b00 (i.e. Output Compare)
- alternating, CCMR2.OC4M=0b101 (Force Active) and CCMR2.OC4M=0b100 (Force Inactive)
Nothing else.
JW
