STM32L011 USART2 and DMA (Continued)

[Archadious]

Previous post: https://community.st.com/t5/stm32-mcus-embedded-software/dma-on-stm32l011f4/td-p/742092

I am working with code on the STM32L011 that uses DMA to read data from USART2.  I received excellent help on this forum before and I'm hoping for the same now.

I'm using a custom PCB  and several colored LEDs for debugging. 
I expect the code to echo data it receives from the USART2 but it does not.  And neither LED is turned on.  It seems that the DMA IRQ handler is not being called.  I believe I'm missing something simple again. 

-A 

[Archadious]

//-----------------------------------------------------------------------------
#include <stdbool.h>
#include <stdio.h>
#include "stm32l0xx.h"
#include "gpio.h"


//-----------------------------------------------------------------------------
#define DMA_BUFFER_SIZE 8
uint8_t dma_buffer[ DMA_BUFFER_SIZE ];
volatile bool flag = false;


//-----------------------------------------------------------------------------
void systemclock_config( void );
void usart2_init( void );
void usart2_write( uint8_t );
void dma_init( void );


//-----------------------------------------------------------------------------
int __io_putchar( int chr ) {

  usart2_write( chr );
  return chr;

};  // end __io_putchar


//-----------------------------------------------------------------------------
int main( void ) {

  systemclock_config( );   // Configure system clock

  // Clear buffer - quick and dirty code
  for ( int i = 0; i < DMA_BUFFER_SIZE; ++i ) { dma_buffer[ i ] = 0x0; };

  usart2_init( );
  dma_init( );

  USART2->CR3 |= USART_CR3_DMAR;  // turn on DMA

  printf( "Start of Application\r\n" );

  while ( 1 ) {

    if ( flag == true ) {

      WHITE_LED_ON;
      flag = false;
      printf( "\r\nReceived '%s'\r\n", dma_buffer );

    };  // end if flag

  };  // end while loop

};  // end main


//-----------------------------------------------------------------------------
void systemclock_config( void ) {

    // Configure the system clock to use HSI at 16 MHz
    RCC->CR |= RCC_CR_HSION;  // Enable HSI
    while (!(RCC->CR & RCC_CR_HSIRDY));  // Wait for HSI to be ready

    RCC->CFGR = 0;  // System clock source is HSI
    SystemCoreClockUpdate();  // Update SystemCoreClock variable

};  // end SystemClock_Config


//-----------------------------------------------------------------------------
void usart2_init( void ) {

  // Enable GPIOA and USART2 clocks
  RCC->IOPENR |= RCC_IOPENR_GPIOAEN;
  RCC->APB1ENR |= RCC_APB1ENR_USART2EN;

  // Configure PA0 as USART2 TR
  GPIOA->MODER &= ~GPIO_MODER_MODE0;  // Clear mode bits
  GPIOA->MODER |= GPIO_MODER_MODE0_1;  // Set PA0 to alternate function mode
  GPIOA->AFR[0] |= ( 4 << GPIO_AFRL_AFSEL0_Pos ); // Set PA0 to AF0 (USART2)

  // Configure PA2 as USART2 TX
  GPIOA->MODER &= ~GPIO_MODER_MODE2;  // Clear mode bits
  GPIOA->MODER |= GPIO_MODER_MODE2_1;  // Set PA2 to alternate function mode
  GPIOA->AFR[0] |= ( 4 << GPIO_AFRL_AFSEL2_Pos );  // Set PA2 to AF4 (USART2)

  // Configure USART2 baud rate, enable TX, enable USART
  USART2->BRR = SystemCoreClock / 9600;  // Set baud rate to 9600 with a 16 MHz clock)

  USART2->CR1 =
    USART_CR1_RE |  // Enable RX
    USART_CR1_TE |  // Enable TX
    USART_CR1_UE;  // Enable USART

};  // end init_usart2


//-----------------------------------------------------------------------------
void usart2_write( uint8_t ch ) {

  while ( !( USART2->ISR & USART_ISR_TXE ) ) { __asm__( "nop" ); };
  USART2->TDR = ( ch & 0xff );  // ensure all 8-bits are transmitted
};  // end usart2_write


//-----------------------------------------------------------------------------
void dma_init( void ) {

    // Enable DMA clock
    RCC->AHBENR |= RCC_AHBENR_DMA1EN;

    DMA1_Channel5->CCR &= ~DMA_CCR_EN;  // turn off DMA1

    DMA1_CSELR->CSELR &= ~DMA_CSELR_C5S;
    DMA1_CSELR->CSELR |= ( 0b0100 << DMA_CSELR_C5S_Pos );

    // Configure DMA for USART2 TX (Channel 5)
    DMA1_Channel5->CPAR = (uint32_t)&USART2->RDR;  // Set peripheral address to USART2 RDR
    DMA1_Channel5->CMAR = (uint32_t)dma_buffer;    // Set memory address to dma_buffer
    DMA1_Channel5->CNDTR = DMA_BUFFER_SIZE - 1; // Set number of data items to transfer

    DMA1_Channel5->CCR =
      DMA_CCR_MINC |  // enable memory increment
      DMA_CCR_TCIE; // |  // enable transfer complete interrupt

    DMA1_Channel5->CCR &= ~DMA_CCR_DIR;  // clear DIR field
    DMA1_Channel5->CCR |= ( 0b11 << DMA_CCR_PL_Pos );

    DMA1_Channel5->CCR &= ~DMA_CCR_MSIZE;  // memory size 8-bits
    DMA1_Channel5->CCR &= ~DMA_CCR_PSIZE;  // usart size 8-bits

    // Enable DMA interrupt in NVIC
    NVIC_EnableIRQ(DMA1_Channel4_5_IRQn);
    NVIC_SetPriority( DMA1_Channel4_5_IRQn, 0x0 );

    DMA1_Channel5->CCR |= DMA_CCR_EN;  // turn on DMA1

};  // end init_dma


//-----------------------------------------------------------------------------
void DMA1_Channel4_5_IRQHandler( void ) {

  ORANGE_LED_ON;

  if ( DMA1->ISR & DMA_ISR_TCIF5 ) {      // Check for transfer complete interrupt flag

    DMA1->IFCR = DMA_IFCR_CTCIF5;     // Clear transfer complete interrupt flag
    DMA1_Channel5->CCR &= ~DMA_CCR_EN;  // Disable DMA Channel 5 after transfer

    flag = true;

  };  // end if

};  // end IRQ