STM32 Series Chapter 21--DMA

Introduction:

DMA stands for Direct Memory Access, which means direct memory access. 
For example, serial port transmission can be sent with or without DMA. Transmission without DMA requires the real-time participation of the microcontroller, which sends data one by one and monitors it. However, if DMA is used, after setting the starting address, data size and other parameters, a dedicated DMA module will directly send data, and the microcontroller does not need to participate in the transmission process. After the transmission, an interrupt will be generated to inform the microcontroller. It can be seen that using DMA can save microcontroller resources and allow the microcontroller to do more things at the same time. 
STM32 has up to 2 DMA controllers (DMA2 only exists in large-capacity products), DMA1 has 7 channels (channel 1 to channel 7). DMA2 has 5 channels (channel 1 to channel 5). Each channel is dedicated to managing requests for memory access from one or more peripherals. There is also an arbitration to coordinate the priority of each DMA request.

Request List:

Request list of 7 channels of DMA1: 

DMA2 request queue for 5 channels 

CODE:

Use DMA to send serial port.

//dma.c#include "dma.h"DMA_InitTypeDef DMA_InitStructure;u16 DMA1_MEM_LEN;//Save the length of each data transfer by DMA //Configuration of each channel of DMA1//The transmission form here is fixed, which needs to be modified according to different situations//From memory->peripheral mode/8-bit data width/memory increment mode//DMA_CHx:DMA channel CHx//cpar:peripheral address//cmar:memory address//cndtr:data transfer amount void MYDMA_Config(DMA_Channel_TypeDef* DMA_CHx,u32 cpar,u32 cmar,u16 cndtr)
{
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE); //Enable DMA transmission
  DMA_DeInit(DMA_CHx); //Reset DMA channel 1 register to default value
    DMA1_MEM_LEN=cndtr;
    DMA_InitStructure.DMA_PeripheralBaseAddr = cpar; //DMA peripheral base address
    DMA_InitStructure.DMA_MemoryBaseAddr = cmar; //DMA memory base address
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST; //Data transmission direction, read from memory and send to peripherals
    DMA_InitStructure.DMA_BufferSize = cndtr; //DMA channel DMA buffer size
    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable; //Peripheral address register remains unchanged
    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable; //Memory address register increment
    DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte; //Data width is 8 bits
    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte; //Data width is 8 bits
    DMA_InitStructure.DMA_Mode = DMA_Mode_Normal; //Work in normal mode
    DMA_InitStructure.DMA_Priority = DMA_Priority_Medium; //DMA channel x has medium priority 
    DMA_InitStructure.DMA_M2M = DMA_M2M_Disable; //DMA channel x is not set for memory to memory transfer
    DMA_Init(DMA_CHx, &DMA_InitStructure); //Initialize the registers identified by the DMA channel USART1_Tx_DMA_Channel according to the parameters specified in DMA_InitStruct} 
// Enable a DMA transfer void MYDMA_Enable(DMA_Channel_TypeDef*DMA_CHx)
{ 
    DMA_Cmd(DMA_CHx, DISABLE ); //Disable the channel indicated by USART1 TX DMA1      
    DMA_SetCurrDataCounter(DMA_CHx,DMA1_MEM_LEN); //DMA channel DMA buffer size
    DMA_Cmd(DMA_CHx, ENABLE); //Enable the channel indicated by USART1 TX DMA1 }   

main.c
#include "led.h"#include "delay.h"#include "key.h"#include "sys.h"#include "lcd.h"#include "usart.h" #include "dma.h"#define SEND_BUF_SIZE 8200 //Send data length, preferably equal to an integer multiple of sizeof(TEXT_TO_SEND)+2.u8 SendBuff[SEND_BUF_SIZE]; //Send data buffer const u8 TEXT_TO_SEND[]={"ALIENTEK WarShip STM32F1 DMA Serial Port Experiment"}; int main(void)
 {   
    u16 i; u8 t=0; u8 j,mask=0; float pro=0;//Progress
    delay_init(); //delay function initialization     
  NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2); //Set the interrupt priority group to group 2: 2-bit preemption priority, 2-bit response priority
    uart_init(115200); //Serial port initialized to 115200
    LED_Init(); //Initialize the hardware interface connected to the LED
    LCD_Init(); //Initialize LCD    
    KEY_Init(); //Key initialization         
    MYDMA_Config(DMA1_Channel4,(u32)&USART1->DR,(u32)SendBuff,SEND_BUF_SIZE);//DMA1 channel 4, peripheral is set to serial port 1, memory is SendBuff, length is SEND_BUF_SIZE.
    POINT_COLOR=RED; //Set the font to red 
    LCD_ShowString(30,50,200,16,16,"WarShip STM32");    
    LCD_ShowString(30,70,200,16,16,"DMA TEST"); 
    LCD_ShowString(30,90,200,16,16,"ATOM@ALIENTEK");
    LCD_ShowString(30,110,200,16,16,"2015/1/15");   
    LCD_ShowString(30,130,200,16,16,"KEY0:Start"); //Display prompt information    
    j=sizeof(TEXT_TO_SEND);    
    for(i=0;i=j)//Add line break
        { if(mask)
            {
                SendBuff[i]=0x0a;
                t=0;
            }else 
            {
                SendBuff[i]=0x0d;
                mask++;
            }   
        } else //Copy TEXT_TO_SEND statement
        {
            mask=0;
            SendBuff[i]=TEXT_TO_SEND[t];
            t++;
        }          
    }        
    POINT_COLOR=BLUE; //Set the font to blue    
    i=0; while(1)
    {
        t=KEY_Scan(0); if(t==KEY0_PRES)//KEY0 is pressed
        {
            LCD_ShowString(30,150,200,16,16,"Start Transimit....");
            LCD_ShowString(30,170,200,16,16," %");//Display the percent sign
            printf("\r\nDMA DATA:\r\n");        
          USART_DMACmd(USART1,USART_DMAReq_Tx,ENABLE); //Enable DMA transmission of serial port 1      
            MYDMA_Enable(DMA1_Channel4); //Start a DMA transfer!      
            //Wait for DMA transfer to complete, now we can do something else, turn on the light
            //In actual applications, other tasks can be performed during data transmission
            while(1)
            { if(DMA_GetFlagStatus(DMA1_FLAG_TC4)!=RESET) //Judge whether the transmission of channel 4 is completed
                {
                    DMA_ClearFlag(DMA1_FLAG_TC4); //Clear channel 4 transfer completion flag
                    break; 
            }
                pro=DMA_GetCurrDataCounter(DMA1_Channel4); //Get the current amount of data remaining
                pro=1-pro/SEND_BUF_SIZE; //get the percentage   
                pro*=100; //Expand 100 times
                LCD_ShowNum(30,170,pro,3,16);     
            }               
            LCD_ShowNum(30,170,100,3,16); //Display 100%     
            LCD_ShowString(30,150,200,16,16,"Transimit Finished!");//Prompt that the transmission is completed
        }
        i++;
        delay_ms(10); if(i==20)
        {
            LED0=!LED0; //Prompt that the system is running   
            i=0;
        }          
    }
}