spi_slave_example.cpp

#include "application.h"

SYSTEM_MODE(MANUAL);


/* Define either MASTER or SLAVE operating mode */
//#define MASTER
#define SLAVE

static uint8_t rx_buffer[64];
static uint8_t tx_buffer[64];
static volatile uint32_t select_state = 0x00;
static volatile uint32_t transfer_state = 0x00;

void onTransferFinished() {
    digitalWriteFast(A0, HIGH);
    transfer_state = 1;
}

/* *********************************************************************************************************** */
#ifdef SLAVE

void onSelect(uint8_t state) {
    if (state)
        select_state = state;
}

/* executes once at startup */
void setup() {
    Serial.begin(9600);
    SPI.onSelect(onSelect);
    SPI.begin(SPI_MODE_SLAVE, A2);
    memset(rx_buffer, 0, sizeof(rx_buffer));
    for (int i = 0; i < sizeof(tx_buffer); i++)
        tx_buffer[i] = (uint8_t)i;
}

/* executes continuously after setup() runs */
void loop() {
    while (1) {
        while(select_state == 0);
        select_state = 0;

        transfer_state = 0;
        SPI.transfer(tx_buffer, rx_buffer, sizeof(rx_buffer), onTransferFinished);
        while(transfer_state == 0);
        if (SPI.available() > 0) {
            Serial.printf("Received %d (0x%02x) bytes", SPI.available(), SPI.available());
            Serial.println();
            for (int i = 0; i < SPI.available(); i++) {
                Serial.printf("%02x ", rx_buffer[i]);
            }
            Serial.println();

            // if (rx_buffer[transferLength - 1] != 0x00) {
            //     Serial.println("Error");
            //     while(true);
            // }
        }
    }
}
/* *********************************************************************************************************** */
#else
/* *********************************************************************************************************** */
static int random_range(int minVal, int maxVal)
{
    return rand() % (maxVal-minVal+1) + minVal;
}

/* executes once at startup */
void setup() {
    Serial.begin(9600);
    SPI.begin(SPI_MODE_MASTER, A2);
    memset(rx_buffer, 0, sizeof(rx_buffer));
    memset(tx_buffer, 0, sizeof(tx_buffer));

    uint32_t seed = millis(); 
    srand(seed);
}

/* executes continuously after setup() runs */
void loop() {
    while (1) {
        int transferLength = random_range(1, sizeof(tx_buffer));
        for (int i = 0; i < transferLength; i++)
            tx_buffer[i] = (uint8_t)(transferLength - i - 1);

        memset(rx_buffer, 0, sizeof(rx_buffer));

        digitalWrite(A2, LOW);
        delay(1);

        transfer_state = 0;
        SPI.transfer(tx_buffer, rx_buffer, transferLength, onTransferFinished);
        while(transfer_state == 0);

        digitalWrite(A2, HIGH);

        Serial.printf("Sent %d (0x%02x) bytes, got back:", transferLength, transferLength);
        Serial.println();
        for (int i = 0; i < transferLength; i++) {
            Serial.printf("%02x ", rx_buffer[i]);
        }
        Serial.println();

        if (rx_buffer[transferLength - 1] != (uint8_t)(transferLength - 1)) {
            Serial.println("Error");
            delay(1000);
        }

        delay(100);
    }
}
/* *********************************************************************************************************** */
#endif