[RP2350_ W6100] Arduino IDE에서 SPI DMA 사용하기

RP2350의 최대 SPI클럭은 시스템 클럭의 1/2 인 75Mhz 이다. 75Mhz로 동작하는 SPI슬레이브는 잘 없을것 같고 1/4 인 37.5Mhz가 적당할것 같다.

Arduino IDE 개발환에서 RP2350의 SPI 전송률 테스트 하면 데이터 전송 간격이 1.2us 정도로 측정 된다.

 

#define _SYS_CLK_           (150000000)

void setup()
{
  Serial.begin(115200);
  Serial.println("SPI tst..");
  
  pinMode(PIN_OUT, OUTPUT);
  digitalWrite(PIN_OUT, 1);
  delay(2000);

  SPI.begin();
  
  SPI.beginTransaction(SPISettings(_SYS_CLK_/4, MSBFIRST, SPI_MODE0));  
}


uint8_t buf[3] = {1, 0xF0, 0x0F};

void loop() {
  SPI.transfer(buf, sizeof(buf));
  SPI.transfer(buf, sizeof(buf));
  delay(10);
}

 

 

테스트 결과 Arduino에서는 역시 SPI Byte 데이터 전송 지연시간이 720ns로 상당히 느리다.

 

---

고속의 데이터 전송을 위해서는 DMA가 필요한데 RP2040에서 SPI DMA 테스트를 진행 해 보자.
 
 
DMA 초기화 함수

#include <SPI.h>
#include "hardware/dma.h"

int32_t            dma_tx_channel;
dma_channel_config dma_tx_config;

#define SPI_PORT  spi0

static uint dma_tx;
static uint dma_rx;
static dma_channel_config dma_channel_config_tx;
static dma_channel_config dma_channel_config_rx;


#define SPI_X spi0

bool initDMA(bool ctrl_cs)
{
  dma_tx = dma_claim_unused_channel(true);
  dma_rx = dma_claim_unused_channel(true);

  dma_channel_config_tx = dma_channel_get_default_config(dma_tx);
  channel_config_set_transfer_data_size(&dma_channel_config_tx, DMA_SIZE_8);
  channel_config_set_dreq(&dma_channel_config_tx, DREQ_SPI0_TX);

  // We set the inbound DMA to transfer from the SPI receive FIFO to a memory buffer paced by the SPI RX FIFO DREQ
  // We coinfigure the read address to remain unchanged for each element, but the write
  // address to increment (so data is written throughout the buffer)
  dma_channel_config_rx = dma_channel_get_default_config(dma_rx);
  channel_config_set_transfer_data_size(&dma_channel_config_rx, DMA_SIZE_8);
  channel_config_set_dreq(&dma_channel_config_rx, DREQ_SPI0_RX);
  channel_config_set_read_increment(&dma_channel_config_rx, false);
  channel_config_set_write_increment(&dma_channel_config_rx, true);

  return true;
}

 

 

 

 

 

RP2350 SPI DMA Write 코드

void spi_write_dma(uint8_t *pBuf, uint16_t len)
{
    uint8_t dummy_data;

    channel_config_set_read_increment(&dma_channel_config_tx, true);
    channel_config_set_write_increment(&dma_channel_config_tx, false);
    dma_channel_configure(dma_tx, &dma_channel_config_tx,
                          &spi_get_hw(SPI_PORT)->dr, // write address
                          pBuf,                      // read address
                          len,                       // element count (each element is of size transfer_data_size)
                          false);                    // don't start yet

    channel_config_set_read_increment(&dma_channel_config_rx, false);
    channel_config_set_write_increment(&dma_channel_config_rx, false);
    dma_channel_configure(dma_rx, &dma_channel_config_rx,
                          &dummy_data,               // write address
                          &spi_get_hw(SPI_PORT)->dr, // read address
                          len,                       // element count (each element is of size transfer_data_size)
                          false);                    // don't start yet

    dma_start_channel_mask((1u << dma_tx) | (1u << dma_rx));
    dma_channel_wait_for_finish_blocking(dma_rx);
}

 

 

 

 

RP2350 SPI DMA 테스트 코드

#define _SYS_CLK_           (150000000)

void setup()
{
  Serial.begin(115200);
  Serial.println("SPI tst..");
  
  pinMode(PIN_OUT, OUTPUT);
  digitalWrite(PIN_OUT, 1);

  delay(2000);
  
  initDMA();
  SPI.begin();

  SPI.beginTransaction(SPISettings(_SYS_CLK_/4, MSBFIRST, SPI_MODE0));  
}


uint8_t buf[3] = {1, 0xF0, 0x0F};

void loop() {
//  SPI.transfer(buf, sizeof(buf));
//  SPI.transfer(buf, sizeof(buf));

	spi_write_dma(buf, 2);	
	spi_write_dma(buf, 2);

    delay(10); 
}

 

 

 

DMA를 사용하면 SPI 전송 간격이 48ns 정도로 상당히 빨라지는 것을 확인 할 수 있다.