spi_peripheral_earle.ino

#include <SPI.h>
#include <SPISlave.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Wire.h>

// WARNING
/*
this basically doesn't work: Earle Core treats SPI transfers 
like UART, i.e. it does minimal listening to CS pin to delineate packets
oddball stuff, I'm set to write it barebones... 
*/

#define PIN_DEBUG 0


// OLED 
#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

#define X_POS 0
#define Y_POS 0
#define TXT_SIZE 1

// even for displays with i.e. "0x78" printed on the back, 
// the address that works is 0x3C, IDK 
#define SCREEN_ADDRESS 0x3C

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire1);

// warning: is blocking, takes ~ 33ms ! 
void displayPrint(String msg){
  display.clearDisplay();
  display.setCursor(X_POS, Y_POS);
  display.print(msg);
  display.display();
}

void displaySetup(void){
  Wire1.setSDA(2);
  Wire1.setSCL(3);

  // initialize the screen,
  // oddly, SWITCHCAPVCC is the option that works even though OLED is hooked to 5V 
  display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS);
  display.clearDisplay();
  display.display();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(TXT_SIZE);
  display.setTextWrap(true);
  display.dim(false);
  displayPrint("bonjour...");
}


// SPI 
SPISettings settings(1000000, MSBFIRST, SPI_MODE0);

uint8_t txBuffer[1024];
volatile uint32_t rxCount = 0;
volatile uint32_t rxSize = 0;

// fires when we get data, I presume ?
// byte rxBuffer[1024];
// this *is unrelated to the CS pin* but should be ! 
// it actually fires basically every data chunk... 
void onRx(uint8_t* data, size_t len){
  // actually, for the echo we can copy 
  // directly across, non ? 
  // digitalWrite(PIN_DEBUG, HIGH);
  // memcpy(txBuffer, data, len);
  rxCount ++;
  if(len > rxSize) rxSize = len;

  // shifty shifty 
  // digitalWrite(PIN_DEBUG, LOW);
}

// fires at the end of a transaction ?
void onTxComplete(void){
  SPISlave1.setData((uint8_t*)txBuffer, 32);
  digitalWrite(PIN_DEBUG, !digitalRead(PIN_DEBUG));
}

void setup(void){
  // a debug light and pin, 
  pinMode(PIN_DEBUG, OUTPUT);
  digitalWrite(PIN_DEBUG, LOW);

  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, LOW);

  // the display setup 
  displaySetup();

  // fill our demo buffer 
  for(uint16_t i = 0; i < 1024; i ++){
    txBuffer[i] = i;
  }
  SPISlave1.setData((uint8_t*)txBuffer, 32);

  // pin config (2040 GPIO Nums)
  SPISlave1.setCS(13);
  SPISlave1.setSCK(10);
  SPISlave1.setRX(12);
  SPISlave1.setTX(11);

  // callbacks 
  SPISlave1.onDataRecv(onRx);
  SPISlave1.onDataSent(onTxComplete);

  // startup 
  SPISlave1.begin(settings);
}

uint32_t lastUpdate = 0;
uint32_t updateInterval = 200;

void loop(void){
  if(lastUpdate + updateInterval < millis()){
    lastUpdate = millis();
    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
    displayPrint(String(rxCount) + "\n" + String(rxSize));
  }
}