说明

SPI共有4根线，MOSI、MISO、CS、CLK，在ESP32中对应规则如下表：
在这里插入图片描述
ESP32共有4个SPI，但是用户能够使用的只有2个SPI，分为VSPI和HSPI。

引脚接口

在ESP32的数据手册中，说明了VSPI和HSPI对应的引脚：

VSPI：
HSPI：

但是比较麻烦的是，ESP官方不知道犯了什么SB毛病，非弄出来个没有丝毫用途的Strapping 管脚，稍不注意，上电瞬间Strapping管脚电平不对，就没法正常启动，导致但凡是有Strapping管脚功能的引脚，大家都不敢使用。
在SPI中也是这样，VSPI和HSPI默认的引脚中，都有作为Strapping管脚的引脚。我们要格外格外的小心。

结合Strapping管脚，将引脚对应整理如下表：

VSPI

引脚	功能	备注
IO23	MOSI
IO19	MISO
IO18	CLK
IO5	CS	Strapping管脚，上电瞬间必须保证上拉

HSPI

引脚	功能	备注
IO13	MOSI
IO12	MISO	Strapping管脚，上电瞬间必须保证下拉
IO14	CLK
IO15	CS	Strapping管脚，上电瞬间必须保证上拉

更改Auduino框架中SPI默认的引脚

在用arduino框架时，其默认的SPI引脚如下：
在这里插入图片描述

除了使用默认的引脚之外，还可以使用其他方式更改默认引脚。官方给出的示例如下：

/* The ESP32 has four SPi buses, however as of right now only two of
 * them are available to use, HSPI and VSPI. Simply using the SPI API 
 * as illustrated in Arduino examples will use VSPI, leaving HSPI unused.
 * 
 * However if we simply intialise two instance of the SPI class for both
 * of these buses both can be used. However when just using these the Arduino
 * way only will actually be outputting at a time.
 * 
 * Logic analyser capture is in the same folder as this example as
 * "multiple_bus_output.png"
 * 
 * created 30/04/2018 by Alistair Symonds
 */
#include <SPI.h>

// Define ALTERNATE_PINS to use non-standard GPIO pins for SPI bus

#ifdef ALTERNATE_PINS
  #define VSPI_MISO   2
  #define VSPI_MOSI   4
  #define VSPI_SCLK   0
  #define VSPI_SS     33

  #define HSPI_MISO   26
  #define HSPI_MOSI   27
  #define HSPI_SCLK   25
  #define HSPI_SS     32
#else
  #define VSPI_MISO   MISO
  #define VSPI_MOSI   MOSI
  #define VSPI_SCLK   SCK
  #define VSPI_SS     SS

  #define HSPI_MISO   12
  #define HSPI_MOSI   13
  #define HSPI_SCLK   14
  #define HSPI_SS     15
#endif

#if CONFIG_IDF_TARGET_ESP32S2 || CONFIG_IDF_TARGET_ESP32S3
#define VSPI FSPI
#endif

static const int spiClk = 1000000; // 1 MHz

//uninitalised pointers to SPI objects
SPIClass * vspi = NULL;
SPIClass * hspi = NULL;

void setup() {
  //initialise two instances of the SPIClass attached to VSPI and HSPI respectively
  vspi = new SPIClass(VSPI);
  hspi = new SPIClass(HSPI);
  
  //clock miso mosi ss

#ifndef ALTERNATE_PINS
  //initialise vspi with default pins
  //SCLK = 18, MISO = 19, MOSI = 23, SS = 5
  vspi->begin();
#else
  //alternatively route through GPIO pins of your choice
  vspi->begin(VSPI_SCLK, VSPI_MISO, VSPI_MOSI, VSPI_SS); //SCLK, MISO, MOSI, SS
#endif

#ifndef ALTERNATE_PINS
  //initialise hspi with default pins
  //SCLK = 14, MISO = 12, MOSI = 13, SS = 15
  hspi->begin();
#else
  //alternatively route through GPIO pins
  hspi->begin(HSPI_SCLK, HSPI_MISO, HSPI_MOSI, HSPI_SS); //SCLK, MISO, MOSI, SS
#endif

  //set up slave select pins as outputs as the Arduino API
  //doesn't handle automatically pulling SS low
  pinMode(vspi->pinSS(), OUTPUT); //VSPI SS
  pinMode(hspi->pinSS(), OUTPUT); //HSPI SS

}

// the loop function runs over and over again until power down or reset
void loop() {
  //use the SPI buses
  spiCommand(vspi, 0b01010101); // junk data to illustrate usage
  spiCommand(hspi, 0b11001100);
  delay(100);
}

void spiCommand(SPIClass *spi, byte data) {
  //use it as you would the regular arduino SPI API
  spi->beginTransaction(SPISettings(spiClk, MSBFIRST, SPI_MODE0));
  digitalWrite(spi->pinSS(), LOW); //pull SS slow to prep other end for transfer
  spi->transfer(data);
  digitalWrite(spi->pinSS(), HIGH); //pull ss high to signify end of data transfer
  spi->endTransaction();
}