E-Ink Photo Camera

#include <Arduino.h>
#include <WiFi.h>
#include <esp_now.h>
#include <esp_wifi.h>
#include "esp_camera.h"

// Seeed Studio XIAO ESP32S3 Sense camera expansion board (OV3660).
#define PWDN_GPIO_NUM     -1
#define RESET_GPIO_NUM    -1
#define XCLK_GPIO_NUM     10
#define SIOD_GPIO_NUM     40
#define SIOC_GPIO_NUM     39
#define Y9_GPIO_NUM       48
#define Y8_GPIO_NUM       11
#define Y7_GPIO_NUM       12
#define Y6_GPIO_NUM       14
#define Y5_GPIO_NUM       16
#define Y4_GPIO_NUM       18
#define Y3_GPIO_NUM       17
#define Y2_GPIO_NUM       15
#define VSYNC_GPIO_NUM    38
#define HREF_GPIO_NUM     47
#define PCLK_GPIO_NUM     13

// The M5Paper receiver sketch must use this same ESP-NOW channel.

static constexpr size_t JPEG_CHUNK_BYTES = 232;

enum PacketType : uint8_t {
  PACKET_CAPTURE_REQUEST = 1,
  PACKET_IMAGE_START = 2,
  PACKET_IMAGE_DATA = 3,
  PACKET_IMAGE_END = 4,
  PACKET_ERROR = 5
};

struct __attribute__((packed)) CameraPacket {
  uint32_t magic;
  uint8_t type;
  uint16_t sequence;
  uint16_t dataLength;
  uint32_t imageLength;
  uint16_t width;
  uint16_t height;
  uint8_t data[JPEG_CHUNK_BYTES];
};

// Forward declarations
bool preparePeer(const uint8_t *mac);
void sendError(const char *message);
void sendCapturedPhoto();
void onEspNowReceive(const esp_now_recv_info_t *info, const uint8_t *incomingData, int length);
void configureCamera();

static constexpr uint8_t ESPNOW_CHANNEL = 1;
static constexpr uint32_t PACKET_MAGIC = 0x5043414DUL; // "PCAM"

static_assert(sizeof(CameraPacket) <= ESP_NOW_MAX_DATA_LEN, "ESP-NOW packet is too large");

volatile bool captureRequested = false;
uint8_t requesterMac[6] = {0};
bool requesterKnown = false;

bool preparePeer(const uint8_t *mac) {
  if (esp_now_is_peer_exist(mac)) {
    return true;
  }

  esp_now_peer_info_t peer = {};
  memcpy(peer.peer_addr, mac, 6);
  peer.channel = ESPNOW_CHANNEL;
  peer.encrypt = false;
  return esp_now_add_peer(&peer) == ESP_OK;
}

void sendError(const char *message) {
  if (!requesterKnown || !preparePeer(requesterMac)) {
    return;
  }

  CameraPacket packet = {};
  packet.magic = PACKET_MAGIC;
  packet.type = PACKET_ERROR;
  packet.dataLength = min(strlen(message), JPEG_CHUNK_BYTES);
  memcpy(packet.data, message, packet.dataLength);
  esp_now_send(requesterMac, reinterpret_cast<const uint8_t *>(&packet),
               offsetof(CameraPacket, data) + packet.dataLength);
}

void sendCapturedPhoto() {
  if (!requesterKnown || !preparePeer(requesterMac)) {
    return;
  }

  camera_fb_t *frame = esp_camera_fb_get();
  if (frame == nullptr) {
    sendError("Camera capture failed");
    return;
  }

  CameraPacket packet = {};
  packet.magic = PACKET_MAGIC;
  packet.type = PACKET_IMAGE_START;
  packet.imageLength = frame->len;
  packet.width = frame->width;
  packet.height = frame->height;
  if (esp_now_send(requesterMac, reinterpret_cast<const uint8_t *>(&packet),
                   offsetof(CameraPacket, data)) != ESP_OK) {
    esp_camera_fb_return(frame);
    return;
  }
  delay(12);

  uint16_t sequence = 0;
  for (size_t offset = 0; offset < frame->len; offset += JPEG_CHUNK_BYTES) {
    const size_t chunkLength = min(JPEG_CHUNK_BYTES, frame->len - offset);
    memset(&packet, 0, sizeof(packet));
    packet.magic = PACKET_MAGIC;
    packet.type = PACKET_IMAGE_DATA;
    packet.sequence = sequence++;
    packet.dataLength = chunkLength;
    memcpy(packet.data, frame->buf + offset, chunkLength);

    // A short gap prevents overflowing the ESP-NOW transmit queue.
    if (esp_now_send(requesterMac, reinterpret_cast<const uint8_t *>(&packet),
                     offsetof(CameraPacket, data) + chunkLength) != ESP_OK) {
      esp_camera_fb_return(frame);
      sendError("Radio transfer failed");
      return;
    }
    delay(4);
  }

  memset(&packet, 0, sizeof(packet));
  packet.magic = PACKET_MAGIC;
  packet.type = PACKET_IMAGE_END;
  packet.sequence = sequence;
  esp_now_send(requesterMac, reinterpret_cast<const uint8_t *>(&packet),
               offsetof(CameraPacket, data));
  esp_camera_fb_return(frame);
}

void onEspNowReceive(const esp_now_recv_info_t *info, const uint8_t *incomingData, int length) {
  if (length < static_cast<int>(offsetof(CameraPacket, data))) {
    return;
  }

  CameraPacket request = {};
  memcpy(&request, incomingData, min(length, static_cast<int>(sizeof(request))));
  if (request.magic != PACKET_MAGIC || request.type != PACKET_CAPTURE_REQUEST) {
    return;
  }

  memcpy(requesterMac, info->src_addr, sizeof(requesterMac));
  requesterKnown = true;
  captureRequested = true;
}

void configureCamera() {
  camera_config_t config = {};
  config.ledc_channel = LEDC_CHANNEL_0;
  config.ledc_timer = LEDC_TIMER_0;
  config.pin_d0 = Y2_GPIO_NUM;
  config.pin_d1 = Y3_GPIO_NUM;
  config.pin_d2 = Y4_GPIO_NUM;
  config.pin_d3 = Y5_GPIO_NUM;
  config.pin_d4 = Y6_GPIO_NUM;
  config.pin_d5 = Y7_GPIO_NUM;
  config.pin_d6 = Y8_GPIO_NUM;
  config.pin_d7 = Y9_GPIO_NUM;
  config.pin_xclk = XCLK_GPIO_NUM;
  config.pin_pclk = PCLK_GPIO_NUM;
  config.pin_vsync = VSYNC_GPIO_NUM;
  config.pin_href = HREF_GPIO_NUM;
  config.pin_sccb_sda = SIOD_GPIO_NUM;
  config.pin_sccb_scl = SIOC_GPIO_NUM;
  config.pin_pwdn = PWDN_GPIO_NUM;
  config.pin_reset = RESET_GPIO_NUM;
  config.xclk_freq_hz = 20000000;
  config.pixel_format = PIXFORMAT_JPEG;
  config.frame_size = FRAMESIZE_QVGA;
  config.jpeg_quality = 18;
  config.fb_count = 1;
  config.grab_mode = CAMERA_GRAB_WHEN_EMPTY;
  config.fb_location = CAMERA_FB_IN_PSRAM;

  if (esp_camera_init(&config) != ESP_OK) {
    while (true) {
      delay(1000);
    }
  }
}

void setup() {
  Serial.begin(115200);
  configureCamera();

  WiFi.mode(WIFI_STA);
  esp_wifi_set_channel(ESPNOW_CHANNEL, WIFI_SECOND_CHAN_NONE);
  if (esp_now_init() != ESP_OK) {
    while (true) {
      delay(1000);
    }
  }
  esp_now_register_recv_cb(onEspNowReceive);
}

void loop() {
  if (captureRequested) {
    captureRequested = false;
    sendCapturedPhoto();
  }
  delay(2);
}