Using printf to USART in IRQ Handler

peter_lanius · ‎2009-12-27

Posted on December 27, 2009 at 19:50

peter_lanius · ‎2011-05-17

Posted on May 17, 2011 at 13:35

Hi,

for test purposes I want to send ADC data to Hyperterminal via USART1. The ADC is configured to send the conversion data from 3 channels via DMA to a memory location and then to generate an Interrupt on EOC.

The code below show my implementation of the IRQHandler and the __putchar() function. I am using CrossWorks 2.0. The __putchar() implementation works fine when using printf() in the main code. But the printf() call in the IRQ does not produce any output on Hyperterminal. If I set a breakpoint at the printf() call and then step through the rest of the IRQHandler, I sometimes get the output to appear.

The ADC is currently triggered every 82ms. The USART1 speed is set at 115200bps.

Not sure if this is a timing issue or an issue with the printf implementation. Any help would be greatly appreciated.

Thanks, Peter

Code:

/** * @brief This function handles ADC1 and ADC2 global interrupts requests. * @param None * @retval None */ void ADC1_2_IRQHandler(void) { float Gyro_XRate, Gyro_YRate, Gyro_Vref; /* Disable ADC1 external trigger */ ADC_ExternalTrigConvCmd(ADC1, DISABLE); /* Disable EOC interrupt */ ADC_ITConfig(ADC1, ADC_IT_EOC, DISABLE); /* Increment the conversions counter */ ADC1Conversions_Number++; /* convert ADC values to float */ Gyro_XRate = (float) ADC1ConvertedValues[0] / ADC_Resolution; Gyro_YRate = (float) ADC1ConvertedValues[1] / ADC_Resolution; Gyro_Vref = (float) ADC1ConvertedValues[2] / ADC_Resolution; /* write ADC converted values to USART1 */ printf(''Gyro X, Y Rate & Vref = %6.4f %6.4f %6.4f nr'', Gyro_XRate, Gyro_YRate, Gyro_Vref); /* Clear ADC1 EOC pending interrupt bit */ ADC_ClearITPendingBit(ADC1, ADC_IT_EOC); /* Enable ADC1 external trigger */ ADC_ExternalTrigConvCmd(ADC1, ENABLE); /* Enable EOC interrupt */ ADC_ITConfig(ADC1, ADC_IT_EOC, ENABLE); }

Code:

/** * @brief Defines USART1 output for printf function. * @param ch: character to output * @retval EOF if a problem occurs */ int __putchar(int ch){ // USART_SendData(USART1, ch); while(USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET); return NULL; }

[ This message was edited by: peter_lanius on 25-12-2009 07:35 ]

[ This message was edited by: peter_lanius on 25-12-2009 07:42 ]

sofiene · ‎2011-05-17

Posted on May 17, 2011 at 13:35

Hi Peter;

It's not recommended to use printf in the interrupt handlers. Your program will stuck in the interrupt routine. I advice you to use it in main using software flags to manage the display. You can also move the computation: ADC1ConvertedValues[X] / ADC_Resolution in main function. So in the interrupt read only the ADC values.

B.R.

M3allem

tomas23 · ‎2011-05-17

Posted on May 17, 2011 at 13:35

Well, two things may be very important: the printf (or any core function of printf) is non-reentrant on small MCUs, thus cannot be called if another printf in main is active.

Second can be very heavy stack and/or heap activity in this function - do you have your heap configured? Try few kB and see.