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USART communication via RXNE interrupt only reads one char

dmg0048
Associate II
Posted on December 11, 2013 at 22:37

Hello ST Community,

I am using a STM32F2 uC for my project, and I have configured an USART interface as an UART by not initializing the clock settings. In order to program the device the UART is connected to I send commands that terminate in <CR><LF> through the interface, then this device automatically sends data without needing the uC to transmit anything else, I would only need to read the data.

I have verified the communication via polling, If I execute a reading function on the infinite loop everything seems to work and I get the responses I expected. However, I need to make this reading procedure via interrupts and here is where I have encountered a few problems.

I enable the RXNE interrupt and set the priority with the NVIC structure, the code jumps to the IRQ handler as expected, however it only jumps once or twice maximum and I can't read the whole response. It's also worth noting thata the characters I read are equal to the first characters I expect from a response from the device, so I believe there is something wrong with the way I am managing this interrupt.

My starting point is an example on the Standard Peripherial Library manual where it explains the procedure to set an interrupt on the USART3 interface. I have also tried to use my polling loop on the IRQ handler function with no success.

Any help or directions are appreciated, thanks in advance!

#usart-tx-rx-interrupt-rxne-uart
3 REPLIES 3
Posted on December 11, 2013 at 22:47

// STM32 USART IRQ TX/RX Loop (USART3 Tx PD.8, Rx PD.9) STM32F2 - sourcer32@gmail.com
#include ''stm32f2xx.h''
volatile char StringLoop[] = ''The quick brown fox jumps over the lazy dog

'';
/**************************************************************************************/
void RCC_Configuration(void)
{
/* --------------------------- System Clocks Configuration -----------------*/
/* USART3 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);
/* GPIOD clock enable */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
}
/**************************************************************************************/
void GPIO_Configuration(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/*-------------------------- GPIO Configuration ----------------------------*/
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOD, &GPIO_InitStructure);
/* Connect USART pins to AF */
GPIO_PinAFConfig(GPIOD, GPIO_PinSource8, GPIO_AF_USART3);
GPIO_PinAFConfig(GPIOD, GPIO_PinSource9, GPIO_AF_USART3);
}
/**************************************************************************************/
void USART3_Configuration(void)
{
USART_InitTypeDef USART_InitStructure;
/* USARTx configuration ------------------------------------------------------*/
/* USARTx configured as follow:
- BaudRate = 9600 baud
- Word Length = 8 Bits
- One Stop Bit
- No parity
- Hardware flow control disabled (RTS and CTS signals)
- Receive and transmit enabled
*/
USART_InitStructure.USART_BaudRate = 9600;
USART_InitStructure.USART_WordLength = USART_WordLength_8b;
USART_InitStructure.USART_StopBits = USART_StopBits_1;
USART_InitStructure.USART_Parity = USART_Parity_No;
USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
USART_Init(USART3, &USART_InitStructure);
USART_Cmd(USART3, ENABLE);
USART_ITConfig(USART3, USART_IT_RXNE | USART_IT_TXE, ENABLE);
}
/**************************************************************************************/
void NVIC_Configuration(void)
{
NVIC_InitTypeDef NVIC_InitStructure;
/* Configure the NVIC Preemption Priority Bits */
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);
/* Enable the USART3 Interrupt */
NVIC_InitStructure.NVIC_IRQChannel = USART3_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
}
/**************************************************************************************/
void USART3_IRQHandler(void)
{
static int tx_index = 0;
static int rx_index = 0;
if (USART_GetITStatus(USART3, USART_IT_TXE) != RESET) // Transmit the string in a loop
{
USART_SendData(USART3, StringLoop[tx_index++]);
if (tx_index >= (sizeof(StringLoop) - 1))
tx_index = 0;
}
if (USART_GetITStatus(USART3, USART_IT_RXNE) != RESET) // Received characters modify string
{
StringLoop[rx_index++] = USART_ReceiveData(USART3);
if (rx_index >= (sizeof(StringLoop) - 1))
rx_index = 0;
}
}
/**************************************************************************************/
int main(void)
{
RCC_Configuration();
GPIO_Configuration();
NVIC_Configuration();
USART3_Configuration();
while(1); // Don't want to exit
}
/**************************************************************************************/

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dmg0048
Associate II
Posted on December 11, 2013 at 23:13

Thank you clive1, that code clears things out a bit. Tomorrow I will implement something similar in my project and see if it works.

dmg0048
Associate II
Posted on December 12, 2013 at 12:51

I used your code to develop one of my own to suit my needs and now I finally have working reading code via the RXNE interrupt. 

I wonder if you could help me with another issue regarding this... in case I wanted to do hardware flow control, would this same IRQ handler you provided work if I used the RTS and CTS signals?