In pervious guides, we took look how to send string using DMA (here), and how to receive characters using interrupt(here). In this guide, we shall use DMA to receive 5 characters and echo back the received character using DMA also.
In this guide, we will cover the following:
- Configure UART for full duplex (TX and RX).
- Code
- Demo
1.1 Configure UART for full duplex with DMA
In part 1 we discussed how to set the uart to send a single character, we shall use the same initialization sequence.
We started by enabling clock access to USART2 and GPIOA port
RCC->APB1ENR|=RCC_APB1ENR_USART2EN; RCC->AHB1ENR|=RCC_AHB1ENR_GPIOAEN;
From part one, we concluded that PA2 is the TX pin and PA3 is the RX pin. Hence, we configure them as alternate function and which alternate function as following:
GPIOA->MODER|=(1<<5);//set bit5 GPIOA->MODER&=~(1<<4);//reset bit4 GPIOA->MODER|=(1<<7);//set bit7 GPIOA->MODER&=~(1<<6);//reset bit6 GPIOA->AFR[0]=0x07700; //ALT7 for UART2 (PA2 and PA3)
Now we need to configure the UART
We starting by setting the baud rate to 9600 as following:
USART2->BRR = 0x0681; //9600 @16MHz
Then we enable the TX and RX of the UART as following
USART2->CR1|=USART_CR1_TE|USART_CR1_RE;
Then enable DMA_TX and DMA_RX in CR3
USART2->CR3|=USART_CR3_DMAR|USART_CR3_DMAT;
Then from CR1 we enable transfer complete interrupt as following
USART2->CR1|=USART_CR1_TCIE;
And finally enable UART from CR1
USART2->CR1|=USART_CR1_UE;
1.2 Configure DMA
For UART DMA transmission, please refer to part 4 of the UART guide (here).
In order to configure DMA to receive data, we need to find which stream and channel of UART_RX is connected to.
From image below, we can see USART2_RX is stream5 channel 4
We start of by enabling clock to DMA as following:
RCC->AHB1ENR |= RCC_AHB1ENR_DMA1EN;
Then disable the current DMA Stream as following
DMA1_Stream5->CR &= ~1; /* disable DMA1 Stream 5 */
while (DMA1_Stream5->CR & 1) {} /* wait until DMA1 Stream 5 is disabled */clear all interrupt for Stream5
DMA1->HIFCR = 0x00003F00; /* clear all interrupt flags of Stream 5 */
Set the peripheral to be UART2->DR, memory address and number of transfer as following
DMA1_Stream5->PAR =(unsigned int)&USART2->DR;
DMA1_Stream5->M0AR = (unsigned int)(d);
DMA1_Stream5->NDTR = sizeof(d);Next we set the following
- set to channel 4
- Memory and peripheral size to 8-bit
- Memory increment
- Circular mode
- Direction peripheral to memory
- Transfer complete interrupt
- Enable the stream
DMA1_Stream5->CR =(1<<27); DMA1_Stream5->CR|=(1<<10)|(1<<8)|(1<<4); DMA1_Stream5->CR|=(1<<0); NVIC_EnableIRQ(DMA1_Stream5_IRQn); /* DMA interrupt enable at NVIC */
Stream 5 interrupt handler
void DMA1_Stream5_IRQHandler(void)
{
if((DMA1->HISR)&(1<<11)) //DMA receive complete
{
done_rec=1; //set receive data to
DMA1->HIFCR|=(1<<11);
}
}in the while loop, if the received data completed, echo back the received data
if(done_rec==1){
sprintf(message,"Received characters are %s \r\n",d);
done_rec=0;
done = 0; /* clear done flag */
DMA1_Stream6_setup((unsigned int)message, (unsigned int)&USART2->DR, strlen(message));
while (done == 0) {} /* wait until DMA data transfer is done */2 Code
Here is the full code
#include "stm32f4xx.h" // Device header
#include "string.h"
#include "stdio.h"
void USART2_init(void);
void DMA1_init(void);
void DMA1_Stream6_setup(unsigned int src, unsigned int dst, int len);
void DMA1_Stream5_setup();
int done = 1;
int done_rec=0;
char d[5];
char message [100]={'\0'};
int main (void) {
USART2_init();
DMA1_init();
DMA1_Stream5_setup();
sprintf(message,"started\r\n");
DMA1_Stream6_setup((unsigned int)message, (unsigned int)&USART2->DR, strlen(message));
while (done == 0) {} /* wait until DMA data transfer is done */
while (1) {
if(done_rec==1){
sprintf(message,"Received characters are %s \r\n",d);
done_rec=0;
done = 0; /* clear done flag */
DMA1_Stream6_setup((unsigned int)message, (unsigned int)&USART2->DR, strlen(message));
while (done == 0) {} /* wait until DMA data transfer is done */
}
}
}
void USART2_init (void) {
RCC->AHB1ENR |= 1; /* enable GPIOA clock */
RCC->APB1ENR |= 0x20000; /* enable USART2 clock */
GPIOA->AFR[0]=0x07700; //ALT7 for UART2
GPIOA->MODER|=0x0080; //enable PA3 as alternate function
GPIOA->MODER|=0x0020; //enable PA2 as alterate fuction
USART2->BRR = 0x0683; /* 9600 baud @ 16 MHz */
USART2->CR1 = 0x0008|(1<<2); /* enable Tx, 8-bit data */
USART2->CR2 = 0x0000; /* 1 stop bit */
USART2->CR3 = 0x0000; /* no flow control */
USART2->CR1 |= 0x2000; /* enable USART2 */
USART2->CR3 |= (1<<7)|(1<<6); /* enable USART2 TX/RX DMA */
USART2->SR = ~0x40; /* clear TC flag */
USART2->CR1 |= 0x0040; /* enable transmit complete interrupt */
NVIC_EnableIRQ(USART2_IRQn); /* USART2 interrupt enable at NVIC */
}
void DMA1_init(void) {
RCC->AHB1ENR |= RCC_AHB1ENR_DMA1EN; /* DMA controller clock enable */
DMA1->HIFCR = 0x003F0000; /* clear all interrupt flags of Stream 6 */
NVIC_EnableIRQ(DMA1_Stream6_IRQn); /* DMA interrupt enable at NVIC */
}
void DMA1_Stream5_setup()
{
RCC->AHB1ENR |= RCC_AHB1ENR_DMA1EN;
DMA1_Stream5->CR &= DMA_SxCR_EN; /* disable DMA1 Stream 5 */
while (DMA1_Stream5->CR & 1) {} /* wait until DMA1 Stream 5 is disabled */
DMA1->HIFCR = 0x00003F00; /* clear all interrupt flags of Stream 5 */
DMA1_Stream5->PAR =(unsigned int)&USART2->DR;
DMA1_Stream5->M0AR = (unsigned int)(d);
DMA1_Stream5->NDTR = sizeof(d);
DMA1_Stream5->CR =(1<<27);
DMA1_Stream5->CR|=(1<<10)|(1<<8)|(1<<4);
DMA1_Stream5->CR|=(1<<0);
NVIC_EnableIRQ(DMA1_Stream5_IRQn); /* DMA interrupt enable at NVIC */
}
void DMA1_Stream6_setup(unsigned int src, unsigned int dst, int len) {
USART2->SR &= ~USART_SR_TC; /* clear UART transmit complete interrupt flag */
DMA1_Stream6->CR &= ~1; /* disable DMA1 Stream 6 */
while (DMA1_Stream6->CR & 1) {} /* wait until DMA1 Stream 6 is disabled */
DMA1->HIFCR = 0x003F0000; /* clear all interrupt flags of Stream 6 */
DMA1_Stream6->PAR = dst;
DMA1_Stream6->M0AR = src;
DMA1_Stream6->NDTR = len;
DMA1_Stream6->CR = 0x08000000; /* USART2_TX on DMA1 Stream6 Channel 4 */
DMA1_Stream6->CR |= 0x00000440; /* data size byte, mem incr, mem-to-peripheral */
DMA1_Stream6->CR |= 0x16; /* enable interrupts DMA_IT_TC | DMA_IT_TE | DMA_IT_DME */
DMA1_Stream6->CR |= 1; /* enable DMA1 Stream 6 */
}
void DMA1_Stream6_IRQHandler(void)
{
if (DMA1->HISR & 0x000C0000) /* if an error occurred */
while(1) {} /* substitute this by error handling */
DMA1->HIFCR = 0x003F0000; /* clear all interrupt flags of Stream 6 */
DMA1_Stream6->CR &= ~0x10; /* disable DMA1 Stream 6 TCIE */
}
void USART2_IRQHandler(void)
{
USART2->SR &= ~0x0040; /* clear transmit complete interrupt flag */
done = 1; /* set the done flag */
}
void DMA1_Stream5_IRQHandler(void)
{
if((DMA1->HISR)&(1<<11)) //DMA receive complete
{
done_rec=1;
DMA1->HIFCR|=(1<<11);
}
}Demo
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