/* p13_1.c Send a string to USART2 by DMA
 *
 * USART2 transmit is on DMA Channel 4.
 * See Reference manual Table 28 RM0360 April 2017.
 *
 * USART2 Tx signal is connected to pin PA2. To see the output of USART2
 * on a PC, you need to use a USB-serial module. Connect the Rx pin of
 * the module to the PA2 pin of the STM32F030 Nucleo board. Make sure
 * the USB-serial module you use has a 3.3V interface.
 *
 * By default, the system clock is running at 8 MHz.
 * The UART is configured for 9600 Baud.
 * PA2 - USART2 TX (AF1)
 *
 * This program was tested with Keil uVision v5.24a with DFP v2.11.0
 */
#include "stm32F0xx.h"

void USART2_init(void);
void DMA1_init(void);
void DMA1_channel4_setup(unsigned int src, unsigned int dst, int len);

int done = 1;

int main(void)
{
	char alphabets[] = "abcdefghijklmnopqrstuvwxyz\n";
	char message[80];
	int i;
	int size = sizeof(alphabets)-1;

	USART2_init();
	DMA1_init();

	while (1) {
		/* prepare the message for transfer */
		for (i = 0; i < size; i++)
			message[i] = alphabets[i];

		/* send the message out by USART2 using DMA */
		while (done == 0) {
		}               /* wait until DMA data transfer is done */
		done = 0;       /* clear done flag */
		DMA1_channel4_setup((unsigned int)message, (unsigned int)&USART2->TDR, size);
	}
}
/*  Initialize UART pins, Baudrate
    The USART2 is configured to send output to pin PA2 at 9600 Baud.
 */
void USART2_init(void)
{
	RCC->AHBENR |= 0x00020000;      /* enable GPIOA clock */
	RCC->APB1ENR |= 0x00020000;     /* enable USART2 clock */

	/* Configure PA2 for USART2_TX */
	GPIOA->AFR[0] &= ~0x0F00;
	GPIOA->AFR[0] |=  0x0100;       /* alt7 for USART2 */
	GPIOA->MODER &= ~0x0030;
	GPIOA->MODER |=  0x0020;        /* enable alternate function for PA2 */

	USART2->BRR = 0x0341;           /* 9600 baud @ 8 MHz */
	USART2->CR1 = 0x0008;           /* enable Tx, 8-bit data */
	USART2->CR2 = 0x0000;           /* 1 stop bit */
	USART2->CR3 = 0x0000;           /* no flow control */
	USART2->CR1 |= 0x0001;          /* enable USART2 */

	USART2->ICR = 0x0040;           /* clear TC flag */
	USART2->CR1 |= 0x0040;          /* enable transmit complete interrupt */

	NVIC_EnableIRQ(USART2_IRQn);    /* USART2 interrupt enable at NVIC */
}


/*  Initialize DMA1 controller
 *  DMA1 controller's clock is enabled and also the DMA interrupt is
 *  enabled in NVIC.
 */
void DMA1_init(void)
{
	RCC->AHBENR |= 0x00000001;                  /* DMA controller clock enable */
	DMA1->IFCR = 0x0000F000;                    /* clear all interrupt flags of Channel 4 */
	NVIC_EnableIRQ(DMA1_Ch4_7_DMA2_Ch3_5_IRQn); /* DMA interrupt enable at NVIC */
}

/*  Set up a DMA transfer for USART2
 *  The USART2 is connected to DMA1 Channel 4. This function sets up the
 *  peripheral register address, memory address, number of transfers,
 *  data size, transfer direction, and DMA interrupts are enabled.
 *  At the end, the DMA controller is enabled and the USART2 transmit
 *  DMA is enabled.
 */
void DMA1_channel4_setup(unsigned int src, unsigned int dst, int len)
{

	DMA1_Channel4->CCR &= ~1;         /* disable DMA1 Channel 4 */
	while (DMA1_Channel4->CCR & 1) {} /* wait until DMA1 Channel 4 is disabled */
	DMA1->IFCR = 0x0000F000;          /* clear all interrupt flags of Channel 4 */
	DMA1_Channel4->CPAR = dst;
	DMA1_Channel4->CMAR = src;
	DMA1_Channel4->CNDTR = len;

	DMA1_Channel4->CCR =  0x00000090; /* data size byte, mem incr, mem-to-peripheral */
	DMA1_Channel4->CCR |= 0x0000000A; /* enable interrupts DMA_IT_TC | DMA_IT_TE */
	DMA1_Channel4->CCR |= 0x00000001; /* enable DMA1 Channel 4 */

	USART2->ICR = 0x0040;             /* clear UART transmit complete interrupt flag */
	USART2->CR3 |= 0x80;              /* enable USART2 transmitter DMA */
}

/*  DMA1 Channel 4-5-6-7 interrupt handler
    This function handles the interrupts from the DMA1 controller Channel4-5-6-7. The error interrupts
    have a placeholder for error handling code. If the interrupt is from DMA data
    transfer complete, the DMA controller is disabled, the interrupt flags are
    cleared.
 */
void DMA1_Channel4_5_6_7_IRQHandler(void)
{
	if (DMA1->ISR & 0x00008000)     /* if an error occurred */
		while (1) {}                /* substitute this by error handling */
	if(DMA1->ISR & 0x0002000){      /* if channel 4 DMA completed */
		DMA1->IFCR = 0x0000F000;    /* clear all interrupt flags of Channel 4 */
		DMA1_Channel4->CCR &= ~0x2; /* disable DMA1 Channel 1 TCIE */
	}
}

/*  USART2 interrupt handler
 *  USART2 transmit complete interrupt is used to set the done flag to signal
 *  the other part of the program that the data transfer is done.
 */
void USART2_IRQHandler(void)
{
	USART2->ICR = 0x0040;           /* clear transmit complete interrupt flag */
	done = 1;                       /* set the done flag */
}