DMA Porter

DMA- hamal
1.
DMA(Direct Memory Access) Direct memory access , You can transfer data from one place to another , It won't occupy us cpu.
CPU Execute instructions according to the content of the code ,
Among these numerous instructions , Some are used for calculation 、 Some are used to control programs 、 Some are used to transfer data . Among them, the instruction to transfer data , especially
Is to transfer a large amount of data , Will take up a lot of CPU. If it is a peripheral A The data of , Pass it to the peripheral B, In fact, this situation does not need CPU Always participate
And , Just in A、B Create a channel between , Let them transmit by themselves . This is it. DMA Purpose of design , Reduce a large number of data transfer instructions .

DMA The main implementation will A The data at is directly transported to B It's about , there A、B It could be memory （ Inside / external SRAM etc. ）, It can also be outside
set up （UART、I2C、SPI、ADC etc. ）, So all the scenarios are as follows ：
 Memory to peripherals
 Peripheral to memory
 Memory to memory

DMA1 Yes 7 Channels ,DMA2 Yes 5 individual passageway , A total of 12 Channels .
You can put DMA Divided into three parts .
after ,DMA The controller processes the requests in turn according to the channel priority , When it's the peripheral's turn , Return the reply signal to the peripheral , The peripheral receives
Answer signal , Release the request , Conduct DMA The data transfer , until DMA End of transmission ;
②DMA passageway ： Different peripherals , To different DMA Send requests through different channels , Pictured 20.1.2 Sum graph 20.1.3 Shown . such as ADC1
Want to use DMA, Should turn to DMA1 The passage of 1 Send a request .DMA1 The passage of 1, It can receive requests from multiple peripherals （ADC1、TIM2_CH3、
TIM4_CH1）, But only one can be received at a time ;
③DMA priority ： When more than one DMA passageway , When a request is sent at the same time , Get software configuration DMA_CCRx Priority of register setting ,
Respond in turn . When the software configuration priorities are the same , Hardware with high priority （ Small channel number ） Priority response . Yes DMA2 In the products of ,DMA1 Has a higher priority than DMA2.

All channels from memory to memory can be used .

Multiple DMA Simultaneous request ：
1. Software phase ：DMA_CCRx DMA Channel configuration register PL-> Set channel priority
2. Hardware phase ： Small channel number has higher priority ,DMA1 Priority is greater than DMA2

Related registers

void DCMI_DMA_Init(void)
{
     
	DMA_InitTypeDef  DMA_InitStructure;
	NVIC_InitTypeDef NVIC_InitStructure;
	
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2,ENABLE);//DMA2 Clock enable  
	DMA_DeInit(DMA2_Stream1);
	while (DMA_GetCmdStatus(DMA2_Stream1) != DISABLE){
    }// wait for DMA2_Stream1 Configurable  
	
	DMA_InitStructure.DMA_Channel = DMA_Channel_1;  // passageway 1 DCMI passageway  
	DMA_InitStructure.DMA_PeripheralBaseAddr = (u32)&DCMI->DR;// The peripheral address is :DCMI->DR  camera 
	DMA_InitStructure.DMA_Memory0BaseAddr = (u32)&LCD->LCD_RAM;//DMA  Memory 0 Address  lcd
	DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;// Peripheral to memory mode   Handling data ： camera ->lcd
	DMA_InitStructure.DMA_BufferSize = 10;// Data transmission volume  
	DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;// Peripheral non incremental mode 
	DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Disable;// Memory incremental mode   close 
	DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Word;// Peripheral data length :32 position 
	DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord ;// Memory data length  16bit 
	DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;//  Use circular mode  
	DMA_InitStructure.DMA_Priority = DMA_Priority_High;// High priority 
	DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Enable; //FIFO Pattern  
	DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_Full;// Use all FIFO 
	DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;// Peripheral burst single transmission 
	DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;// Memory burst single transmission 
	DMA_Init(DMA2_Stream1, &DMA_InitStructure);// initialization DMA Stream
DMA_ITConfig(DMA2_Stream1,DMA_IT_TC,ENABLE);
	NVIC_InitStructure.NVIC_IRQChannel=	DMA2_Stream1_IRQn;
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0;
	NVIC_InitStructure.NVIC_IRQChannelSubPriority=0;
	NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;
	NVIC_Init(&NVIC_InitStructure);	// Initialize... According to the specified parameters VIC register 、 
} 

//DCMI, Start transmission

void DCMI_Start(void)
{
     
	LCD_Scan_Dir(U2D_L2R);	//U2D_L2R // Scan from top to bottom , From left to right , General pattern  
	LCD_Set_Window(0,0,320,240); //LCD Set the display window , If you change the resolution , There needs to be a change 
	LCD_SetCursor(0,0); // Set the cursor  
	LCD_WriteRAM_Prepare();	// Start writing GRAM
	DMA_Cmd(DMA2_Stream1, ENABLE);// Turn on DMA2,Stream1 
	DCMI_CaptureCmd(ENABLE);//DCMI Capture enable  
}
//DCMI, Turn off transmission 
void DCMI_Stop(void)
{
     
	DCMI_CaptureCmd(DISABLE);//DCMI Capture to close  
	while(DCMI->CR&0X01);		// Wait for the end of the transmission  
	DMA_Cmd(DMA2_Stream1,DISABLE);// close DMA2,Stream1
} 
//DCMI Interrupt service function 
void DCMI_IRQHandler(void)
{
    
	if(DCMI_GetITStatus(DCMI_IT_LINE)==SET)// Capture row 
	{
    
		DCMI_ClearITPendingBit(DCMI_IT_LINE);// Clear interrupt  
		ov_frame++;
	}
	
}