Hello everybody.
I want to use the Portenta H7 to realize a very simple but fast OOK transmitter. Therefore I need to generate 10 us rectangular pulses, which I can achieve by utilizing HAL GPIO operations in combination with a timer.
Now the problem: I noticed that although most of the pulses are exactly 10 us, some of them are up to 14 us long, which is a problem for the receiver.
Thinking this might result from the timer overflow, I removed it completely leaving only GPIO bit banging as you can see in the following code example:
//#include "stm32h7xx_hal_gpio.h"
void setup() {
// put your setup code here, to run once:
MX_GPIO_Init(); // Initialize GPIO
}
void loop() {
// put your main code here, to run repeatedly:
HAL_GPIO_WritePin(GPIOH, GPIO_PIN_15, GPIO_PIN_SET); // SET Pin PH15 HIGH
HAL_GPIO_WritePin(GPIOH, GPIO_PIN_15, GPIO_PIN_RESET); // SET Pin PH15 LOW
}
// ------------------------ GPIO Pin Initialization for STM32 ------------------------
void MX_GPIO_Init()
{
/* GPIO Ports Clock Enable */
__HAL_RCC_GPIOH_CLK_ENABLE();
GPIO_InitTypeDef GPIO_InitStruct;
/*Configure GPIO pin : PH15 */
GPIO_InitStruct.Pin = GPIO_PIN_15; // Pin15 -> D0 on arduino portenta
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP; // digital Output, push-pull configuration
GPIO_InitStruct.Speed = GPIO_SPEED_HIGH;
HAL_GPIO_Init(GPIOH, &GPIO_InitStruct); // GPIO-H
}
The result can be seen in image0 in the attachment. The GPIO-toggle works very fast. One cycle takes no more than 50 ns. However, as can be seen in the image0, every 125 us there is a break of about 4 us, where nothing happens. This problem was also discovered here
https://www.raspberrypi.org/forums/viewtopic.php?t=13892
but no solution was found. Since the delays from 10us to 14us are also happening every 125 us I think this might be the cause.
Has anybody an idea what causes those breaks and how to get rid of them?
Greetings
