Arduino uno 上的 SPI 协议

Question

我正在尝试为我的 arduino uno 编写低级 SPI 写入/传输协议。但是我的逻辑分析仪上不断出现超调值 (ascii - 255)。

我真的很感激能帮助我理解我可能错在哪里。

我还注意到关闭（在 SPCR 中重置 SPE）会导致它在下一次迭代的写入/传输过程中随机冻结。

/* SPI Slave Demo
 *
 * SPI pin numbers:
 * SCK   13  // Serial Clock.
 * MISO  12  // Master In Slave Out.
 * MOSI  11  // Master Out Slave In.
 * SS    10  // Slave Select . Arduino SPI pins respond only if SS pulled low by the master
 *
 
 */
#include<stdint.h>  
// SPI port available at port B
#define SPI_SCK  5        // 13
#define SPI_MISO 4        // 12
#define SPI_MOSI 3        // 11
#define SPI_SS   2        // 10


// SPI control register bits
#define MSTR     4
#define SPE      6

// SPI status register bits
#define SPIF     7

#define ENABLE        0x1U
// Buffer to hold data
char dataBuff[500];

// initialize the pins to the modes that support their functionality
void pin_init(){
    Serial.println("PIN init");
    // output pins
    // Set the Direction of the SCLk and MOSI pins as output
    DDRB |= (ENABLE << SPI_SCK) | (ENABLE << SPI_MOSI);
    if( (0x1 & (DDRB >> SPI_SCK) ) && ( 0x1 & (DDRB >> SPI_MOSI) )){
      Serial.println("Output Pins set");
    }

    // Input pins
    // Set the direction of the MISO and SS pins as Outputs
    DDRB &= ~((ENABLE << SPI_MOSI) | (ENABLE << SPI_SS));
    if( ~( (0x1 & (DDRB >> SPI_MOSI) ) && ( 0x1 & (DDRB >> SPI_SS) ) ) ){
      Serial.println("Input Pins set");
    }
    
    
    // Enable Pull up for these pins
    PORTB |= (ENABLE << SPI_MOSI) | (ENABLE << SPI_SS);
}

// Initialize the SPI port
uint8_t spi_init(){
  Serial.println("SPI init");
  // Set the SPI mode as master
  SPCR |= (ENABLE << MSTR);
  // Enable the SPI bit
  SPCR |= (ENABLE << SPE);
  
  if( ( 0x1 & (SPCR >> SPE) ) ){
    Serial.println("SPI opened successfully");
  }
  // return the state of the master setting bit
  return (0x1 & (SPCR >> MSTR));
}

// Write to the SPI data buffer
void writeData(uint8_t* data, uint16_t len){
  Serial.println("In write!");
  // Repeat until all bytes sent
  while(len > 0){
    // write to the DR register
    Serial.print("Writing...\t Amount left: ");
    SPDR = *data++;
    // decrement length
    len--;
    Serial.println(len);
    // Wait for the SPIF bit to be set to indicate
    while(!(SPSR & (1<<SPIF)));
  }
}


// read from the data register
// { #TODO }



// Close the SPI port
void spi_close(){
  // Disable the SPI bit
  SPCR &= ~(ENABLE << SPE);
  if( ! ( 0x1 & (SPCR >> SPE) ) ){
    Serial.println("SPI closed successfully");
  }
}

void setup(){
  // Clear global interrupts
//  cli();
  // Instantiate serial comm
  Serial.begin(9600);
  // Initilize the GPIO Pins
  pin_init();  
  // initialize the SPI protocol
  while( !spi_init() ){
    Serial.println("Error in SPI initialization");
  }
  Serial.println("Setup Done!");
}


void loop(){
//  char* data[10] = {"Hello", "from", "Alex"};

  char* data = "Hello";
  uint16_t dataLen = strlen(data);
  // write 
  writeData((uint8_t*) data, dataLen);

}