ESP32的VSPI和HSPI

说明

SPI共有4根线，MOSI、MISO、CS、CLK，在ESP32中对应规则如下表：

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：

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 

// 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();
}