#include<SPI.h>SPISettingsmySettings(1000000, MSBFIRST, SPI_MODE0, SPI_PERIPHERAL);voidsetup() {  Serial.begin(115200);while (!Serial);  SPI.begin();}voidloop() {uint8_t buf[] = {0x01,0x02,0x03,0x04};  SPI.beginTransaction(mySettings);  SPI.transfer(buf,sizeof(buf));  SPI.endTransaction();    Serial.println("Received:");for (int i=0; i<sizeof(buf); i++) {    Serial.print("0x"); Serial.println(buf[0], HEX);  }delay(100);}