RNode_Firmware_CE/Utilities.h

#include <EEPROM.h>
#include <stddef.h>
#include "LoRa.h"
#include "ROM.h"
#include "Config.h"
#include "Framing.h"
#include "MD5.h"

#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
	#include <avr/wdt.h>
	#include <util/atomic.h>
#elif MCU_VARIANT == MCU_ESP32
	// TODO: Hard reset on ESP32
#endif

uint8_t boot_vector = 0x00;

#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
	uint8_t OPTIBOOT_MCUSR __attribute__ ((section(".noinit")));
	void resetFlagsInit(void) __attribute__ ((naked)) __attribute__ ((used)) __attribute__ ((section (".init0")));
	void resetFlagsInit(void) {
	    __asm__ __volatile__ ("sts %0, r2\n" : "=m" (OPTIBOOT_MCUSR) :);
	}
#elif MCU_VARIANT == MCU_ESP32
	// TODO: Get ESP32 boot flags
#endif

#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
	void led_rx_on()  { digitalWrite(pin_led_rx, HIGH); }
	void led_rx_off() {	digitalWrite(pin_led_rx, LOW); }
	void led_tx_on()  { digitalWrite(pin_led_tx, HIGH); }
	void led_tx_off() { digitalWrite(pin_led_tx, LOW); }
#elif MCU_VARIANT == MCU_ESP32
	void led_rx_on()  { digitalWrite(pin_led_rx, LOW); }
	void led_rx_off() {	digitalWrite(pin_led_rx, HIGH); }
	void led_tx_on()  { digitalWrite(pin_led_tx, LOW); }
	void led_tx_off() { digitalWrite(pin_led_tx, HIGH); }
#endif

void hard_reset(void) {
	#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
		wdt_enable(WDTO_15MS);
		while(true) {
			led_tx_on(); led_rx_off();
		}
	#elif MCU_VARIANT == MCU_ESP32
		ESP.restart();
	#endif
}

void led_indicate_error(int cycles) {
	bool forever = (cycles == 0) ? true : false;
	cycles = forever ? 1 : cycles;
	while(cycles > 0) {
        digitalWrite(pin_led_rx, HIGH);
        digitalWrite(pin_led_tx, LOW);
        delay(100);
        digitalWrite(pin_led_rx, LOW);
        digitalWrite(pin_led_tx, HIGH);
        delay(100);
        if (!forever) cycles--;
    }
    led_rx_off();
    led_tx_off();
}

void led_indicate_boot_error() {
	while (true) {
	    led_tx_on();
	    led_rx_off();
	    delay(10);
	    led_rx_on();
	    led_tx_off();
	    delay(5);
	}
}

void led_indicate_warning(int cycles) {
	bool forever = (cycles == 0) ? true : false;
	cycles = forever ? 1 : cycles;
	digitalWrite(pin_led_tx, HIGH);
	while(cycles > 0) {
        led_tx_off();
        delay(100);
        led_tx_on();
        delay(100);
        if (!forever) cycles--;
    }
   led_tx_off();
}

#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
	void led_indicate_info(int cycles) {
		bool forever = (cycles == 0) ? true : false;
		cycles = forever ? 1 : cycles;
		while(cycles > 0) {
	    led_rx_off();
	    delay(100);
	    led_rx_on();
	    delay(100);
	    if (!forever) cycles--;
	  }
	  led_rx_off();
	}
#elif MCU_VARIANT == MCU_ESP32
	void led_indicate_info(int cycles) {
		bool forever = (cycles == 0) ? true : false;
		cycles = forever ? 1 : cycles;
		while(cycles > 0) {
	    led_tx_off();
	    delay(100);
	    led_tx_on();
	    delay(100);
	    if (!forever) cycles--;
	  }
	  led_tx_off();
	}
#endif


unsigned long led_standby_ticks = 0;
#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
	uint8_t led_standby_min = 1;
	uint8_t led_standby_max = 40;
	unsigned long led_standby_wait = 11000;
#elif MCU_VARIANT == MCU_ESP32
	uint8_t led_standby_min = 200;
	uint8_t led_standby_max = 255;
	uint8_t led_notready_min = 0;
	uint8_t led_notready_max = 255;
	uint8_t led_notready_value = led_notready_min;
	int8_t  led_notready_direction = 0;
	unsigned long led_notready_ticks = 0;
	unsigned long led_standby_wait = 1768;
	unsigned long led_notready_wait = 150;
#endif
uint8_t led_standby_value = led_standby_min;
int8_t  led_standby_direction = 0;

#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
	void led_indicate_standby() {
		led_standby_ticks++;
		if (led_standby_ticks > led_standby_wait) {
			led_standby_ticks = 0;
			if (led_standby_value <= led_standby_min) {
				led_standby_direction = 1;
			} else if (led_standby_value >= led_standby_max) {
				led_standby_direction = -1;
			}
			led_standby_value += led_standby_direction;
			analogWrite(pin_led_rx, led_standby_value);
			led_tx_off();
		}
	}
#elif MCU_VARIANT == MCU_ESP32
	void led_indicate_standby() {
		led_standby_ticks++;
		if (led_standby_ticks > led_standby_wait) {
			led_standby_ticks = 0;
			if (led_standby_value <= led_standby_min) {
				led_standby_direction = 1;
			} else if (led_standby_value >= led_standby_max) {
				led_standby_direction = -1;
			}
			led_standby_value += led_standby_direction;
			if (led_standby_value > 253) {
				led_tx_on();
			} else {
				led_tx_off();
			}
			led_rx_off();

		}
	}
#endif

#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
	void led_indicate_not_ready() {
		led_standby_ticks++;
		if (led_standby_ticks > led_standby_wait) {
			led_standby_ticks = 0;
			if (led_standby_value <= led_standby_min) {
				led_standby_direction = 1;
			} else if (led_standby_value >= led_standby_max) {
				led_standby_direction = -1;
			}
			led_standby_value += led_standby_direction;
			analogWrite(pin_led_tx, led_standby_value);
			led_rx_off();
		}
	}
#elif MCU_VARIANT == MCU_ESP32
	void led_indicate_not_ready() {
		led_notready_ticks++;
		if (led_notready_ticks > led_notready_wait) {
			led_notready_ticks = 0;
			if (led_notready_value <= led_notready_min) {
				led_notready_direction = 1;
			} else if (led_notready_value >= led_notready_max) {
				led_notready_direction = -1;
			}
			led_notready_value += led_notready_direction;
			if (led_notready_value > 128) {
				led_tx_on();
			} else {
				led_tx_off();
			}
			led_rx_off();
		}
	}
#endif

void escapedSerialWrite(uint8_t byte) {
	if (byte == FEND) { Serial.write(FESC); byte = TFEND; }
    if (byte == FESC) { Serial.write(FESC); byte = TFESC; }
    Serial.write(byte);
}

void kiss_indicate_error(uint8_t error_code) {
	Serial.write(FEND);
	Serial.write(CMD_ERROR);
	Serial.write(error_code);
	Serial.write(FEND);
}

void kiss_indicate_radiostate() {
	Serial.write(FEND);
	Serial.write(CMD_RADIO_STATE);
	Serial.write(radio_online);
	Serial.write(FEND);
}

void kiss_indicate_stat_rx() {
	Serial.write(FEND);
	Serial.write(CMD_STAT_RX);
	escapedSerialWrite(stat_rx>>24);
	escapedSerialWrite(stat_rx>>16);
	escapedSerialWrite(stat_rx>>8);
	escapedSerialWrite(stat_rx);
	Serial.write(FEND);
}

void kiss_indicate_stat_tx() {
	Serial.write(FEND);
	Serial.write(CMD_STAT_TX);
	escapedSerialWrite(stat_tx>>24);
	escapedSerialWrite(stat_tx>>16);
	escapedSerialWrite(stat_tx>>8);
	escapedSerialWrite(stat_tx);
	Serial.write(FEND);
}

void kiss_indicate_stat_rssi() {
	uint8_t packet_rssi_val = (uint8_t)(last_rssi+rssi_offset);
	Serial.write(FEND);
	Serial.write(CMD_STAT_RSSI);
	escapedSerialWrite(packet_rssi_val);
	Serial.write(FEND);
}

void kiss_indicate_stat_snr() {
	Serial.write(FEND);
	Serial.write(CMD_STAT_SNR);
	escapedSerialWrite(last_snr_raw);
	Serial.write(FEND);
}

void kiss_indicate_radio_lock() {
	Serial.write(FEND);
	Serial.write(CMD_RADIO_LOCK);
	Serial.write(radio_locked);
	Serial.write(FEND);
}

void kiss_indicate_spreadingfactor() {
	Serial.write(FEND);
	Serial.write(CMD_SF);
	Serial.write((uint8_t)lora_sf);
	Serial.write(FEND);
}

void kiss_indicate_codingrate() {
	Serial.write(FEND);
	Serial.write(CMD_CR);
	Serial.write((uint8_t)lora_cr);
	Serial.write(FEND);
}

void kiss_indicate_implicit_length() {
	Serial.write(FEND);
	Serial.write(CMD_IMPLICIT);
	Serial.write(implicit_l);
	Serial.write(FEND);
}

void kiss_indicate_txpower() {
	Serial.write(FEND);
	Serial.write(CMD_TXPOWER);
	Serial.write((uint8_t)lora_txp);
	Serial.write(FEND);
}

void kiss_indicate_bandwidth() {
	Serial.write(FEND);
	Serial.write(CMD_BANDWIDTH);
	escapedSerialWrite(lora_bw>>24);
	escapedSerialWrite(lora_bw>>16);
	escapedSerialWrite(lora_bw>>8);
	escapedSerialWrite(lora_bw);
	Serial.write(FEND);
}

void kiss_indicate_frequency() {
	Serial.write(FEND);
	Serial.write(CMD_FREQUENCY);
	escapedSerialWrite(lora_freq>>24);
	escapedSerialWrite(lora_freq>>16);
	escapedSerialWrite(lora_freq>>8);
	escapedSerialWrite(lora_freq);
	Serial.write(FEND);
}

void kiss_indicate_random(uint8_t byte) {
	Serial.write(FEND);
	Serial.write(CMD_RANDOM);
	Serial.write(byte);
	Serial.write(FEND);
}

void kiss_indicate_ready() {
	Serial.write(FEND);
	Serial.write(CMD_READY);
	Serial.write(0x01);
	Serial.write(FEND);
}

void kiss_indicate_not_ready() {
	Serial.write(FEND);
	Serial.write(CMD_READY);
	Serial.write(0x00);
	Serial.write(FEND);
}

void kiss_indicate_promisc() {
	Serial.write(FEND);
	Serial.write(CMD_PROMISC);
	if (promisc) {
		Serial.write(0x01);
	} else {
		Serial.write(0x00);
	}
	Serial.write(FEND);
}

void kiss_indicate_detect() {
	Serial.write(FEND);
	Serial.write(CMD_DETECT);
	Serial.write(DETECT_RESP);
	Serial.write(FEND);
}

void kiss_indicate_version() {
	Serial.write(FEND);
	Serial.write(CMD_FW_VERSION);
	Serial.write(MAJ_VERS);
	Serial.write(MIN_VERS);
	Serial.write(FEND);
}

void kiss_indicate_platform() {
	Serial.write(FEND);
	Serial.write(CMD_PLATFORM);
	Serial.write(PLATFORM);
	Serial.write(FEND);
}

void kiss_indicate_mcu() {
	Serial.write(FEND);
	Serial.write(CMD_MCU);
	Serial.write(MCU_VARIANT);
	Serial.write(FEND);
}

inline bool isSplitPacket(uint8_t header) {
	return (header & FLAG_SPLIT);
}

inline uint8_t packetSequence(uint8_t header) {
	return header >> 4;
}

inline void getPacketData(int len) {
	while (len--) {
		pbuf[read_len++] = LoRa.read();
	}
}

void setSpreadingFactor() {
	if (radio_online) LoRa.setSpreadingFactor(lora_sf);
}

void setCodingRate() {
	if (radio_online) LoRa.setCodingRate4(lora_cr);
}

void set_implicit_length(uint8_t len) {
	implicit_l = len;
	if (implicit_l != 0) {
		implicit = true;
	} else {
		implicit = false;
	}
}

void setTXPower() {
	if (radio_online) {
		if (model == MODEL_A4) LoRa.setTxPower(lora_txp, PA_OUTPUT_RFO_PIN);
		if (model == MODEL_A9) LoRa.setTxPower(lora_txp, PA_OUTPUT_PA_BOOST_PIN);
	}
}


void getBandwidth() {
	if (radio_online) {
			lora_bw = LoRa.getSignalBandwidth();
	}
}

void setBandwidth() {
	if (radio_online) {
		LoRa.setSignalBandwidth(lora_bw);
		getBandwidth();
	}
}

void getFrequency() {
	if (radio_online) {
		lora_freq = LoRa.getFrequency();
	}
}

void setFrequency() {
	if (radio_online) {
		LoRa.setFrequency(lora_freq);
		getFrequency();
	}
}

uint8_t getRandom() {
	if (radio_online) {
		return LoRa.random();
	} else {
		return 0x00;
	}
}

void promisc_enable() {
	promisc = true;
}

void promisc_disable() {
	promisc = false;
}

bool eeprom_info_locked() {
	uint8_t lock_byte = EEPROM.read(eeprom_addr(ADDR_INFO_LOCK));
	if (lock_byte == INFO_LOCK_BYTE) {
		return true;
	} else {
		return false;
	}
}

void eeprom_dump_info() {
	for (int addr = ADDR_PRODUCT; addr <= ADDR_INFO_LOCK; addr++) {
		uint8_t byte = EEPROM.read(eeprom_addr(addr));
		escapedSerialWrite(byte);
	}
}

void eeprom_dump_config() {
	for (int addr = ADDR_CONF_SF; addr <= ADDR_CONF_OK; addr++) {
		uint8_t byte = EEPROM.read(eeprom_addr(addr));
		escapedSerialWrite(byte);
	}
}

void eeprom_dump_all() {
	for (int addr = 0; addr < EEPROM_RESERVED; addr++) {
		uint8_t byte = EEPROM.read(eeprom_addr(addr));
		escapedSerialWrite(byte);
	}
}

void kiss_dump_eeprom() {
	Serial.write(FEND);
	Serial.write(CMD_ROM_READ);
	eeprom_dump_all();
	Serial.write(FEND);
}

void eeprom_update(int mapped_addr, uint8_t byte) {
	#if MCU_VARIANT == MCU_1284P || MCU_VARIANT == MCU_2560
		EEPROM.update(mapped_addr, byte);
	#elif MCU_VARIANT == MCU_ESP32
		if (EEPROM.read(mapped_addr) != byte) {
			EEPROM.write(mapped_addr, byte);
			EEPROM.commit();
		}
	#endif

}

void eeprom_write(uint8_t addr, uint8_t byte) {
	if (!eeprom_info_locked() && addr >= 0 && addr < EEPROM_RESERVED) {
		eeprom_update(eeprom_addr(addr), byte);
	} else {
		kiss_indicate_error(ERROR_EEPROM_LOCKED);
	}
}

void eeprom_erase() {
	for (int addr = 0; addr < EEPROM_RESERVED; addr++) {
		eeprom_update(eeprom_addr(addr), 0xFF);
	}
	hard_reset();
}

bool eeprom_lock_set() {
	if (EEPROM.read(eeprom_addr(ADDR_INFO_LOCK)) == INFO_LOCK_BYTE) {
		return true;
	} else {
		return false;
	}
}

bool eeprom_product_valid() {
	uint8_t rval = EEPROM.read(eeprom_addr(ADDR_PRODUCT));
	if (rval == PRODUCT_RNODE || rval == PRODUCT_HMBRW || rval == PRODUCT_TBEAM) {
		return true;
	} else {
		return false;
	}
}

bool eeprom_model_valid() {
	model = EEPROM.read(eeprom_addr(ADDR_MODEL));
	if (model == MODEL_A4 || model == MODEL_A9 || model == MODEL_FF || model == MODEL_E4 || model == MODEL_E9) {
		return true;
	} else {
		return false;
	}
}

bool eeprom_hwrev_valid() {
	hwrev = EEPROM.read(eeprom_addr(ADDR_HW_REV));
	if (hwrev != 0x00 && hwrev != 0xFF) {
		return true;
	} else {
		return false;
	}
}

bool eeprom_checksum_valid() {
	char *data = (char*)malloc(CHECKSUMMED_SIZE);
	for (uint8_t  i = 0; i < CHECKSUMMED_SIZE; i++) {
		char byte = EEPROM.read(eeprom_addr(i));
		data[i] = byte;
	}
	
	unsigned char *hash = MD5::make_hash(data, CHECKSUMMED_SIZE);
	bool checksum_valid = true;
	for (uint8_t i = 0; i < 16; i++) {
		uint8_t stored_chk_byte = EEPROM.read(eeprom_addr(ADDR_CHKSUM+i));
		uint8_t calced_chk_byte = (uint8_t)hash[i];
		if (stored_chk_byte != calced_chk_byte) {
			checksum_valid = false;
		}
	}

	free(hash);
	free(data);
	return checksum_valid;
}

bool eeprom_have_conf() {
	if (EEPROM.read(eeprom_addr(ADDR_CONF_OK)) == CONF_OK_BYTE) {
		return true;
	} else {
		return false;
	}
}

void eeprom_conf_load() {
	if (eeprom_have_conf()) {
		lora_sf = EEPROM.read(eeprom_addr(ADDR_CONF_SF));
		lora_cr = EEPROM.read(eeprom_addr(ADDR_CONF_CR));
		lora_txp = EEPROM.read(eeprom_addr(ADDR_CONF_TXP));
		lora_freq = (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_FREQ)+0x00) << 24 | (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_FREQ)+0x01) << 16 | (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_FREQ)+0x02) << 8 | (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_FREQ)+0x03);
		lora_bw = (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_BW)+0x00) << 24 | (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_BW)+0x01) << 16 | (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_BW)+0x02) << 8 | (uint32_t)EEPROM.read(eeprom_addr(ADDR_CONF_BW)+0x03);
	}
}

void eeprom_conf_save() {
	if (hw_ready && radio_online) {
		eeprom_update(eeprom_addr(ADDR_CONF_SF), lora_sf);
		eeprom_update(eeprom_addr(ADDR_CONF_CR), lora_cr);
		eeprom_update(eeprom_addr(ADDR_CONF_TXP), lora_txp);

		eeprom_update(eeprom_addr(ADDR_CONF_BW)+0x00, lora_bw>>24);
		eeprom_update(eeprom_addr(ADDR_CONF_BW)+0x01, lora_bw>>16);
		eeprom_update(eeprom_addr(ADDR_CONF_BW)+0x02, lora_bw>>8);
		eeprom_update(eeprom_addr(ADDR_CONF_BW)+0x03, lora_bw);

		eeprom_update(eeprom_addr(ADDR_CONF_FREQ)+0x00, lora_freq>>24);
		eeprom_update(eeprom_addr(ADDR_CONF_FREQ)+0x01, lora_freq>>16);
		eeprom_update(eeprom_addr(ADDR_CONF_FREQ)+0x02, lora_freq>>8);
		eeprom_update(eeprom_addr(ADDR_CONF_FREQ)+0x03, lora_freq);

		eeprom_update(eeprom_addr(ADDR_CONF_OK), CONF_OK_BYTE);
		led_indicate_info(10);
	} else {
		led_indicate_warning(10);
	}
}

void eeprom_conf_delete() {
	eeprom_update(eeprom_addr(ADDR_CONF_OK), 0x00);
}

void unlock_rom() {
	led_indicate_error(50);
	eeprom_erase();
}

typedef struct FIFOBuffer
{
  unsigned char *begin;
  unsigned char *end;
  unsigned char * volatile head;
  unsigned char * volatile tail;
} FIFOBuffer;

inline bool fifo_isempty(const FIFOBuffer *f) {
  return f->head == f->tail;
}

inline bool fifo_isfull(const FIFOBuffer *f) {
  return ((f->head == f->begin) && (f->tail == f->end)) || (f->tail == f->head - 1);
}

inline void fifo_push(FIFOBuffer *f, unsigned char c) {
  *(f->tail) = c;
  
  if (f->tail == f->end) {
    f->tail = f->begin;
  } else {
    f->tail++;
  }
}

inline unsigned char fifo_pop(FIFOBuffer *f) {
  if(f->head == f->end) {
    f->head = f->begin;
    return *(f->end);
  } else {
    return *(f->head++);
  }
}

inline void fifo_flush(FIFOBuffer *f) {
  f->head = f->tail;
}

#if MCU_VARIANT != MCU_ESP32
	static inline bool fifo_isempty_locked(const FIFOBuffer *f) {
	  bool result;
	  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
	    result = fifo_isempty(f);
	  }
	  return result;
	}

	static inline bool fifo_isfull_locked(const FIFOBuffer *f) {
	  bool result;
	  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
	    result = fifo_isfull(f);
	  }
	  return result;
	}

	static inline void fifo_push_locked(FIFOBuffer *f, unsigned char c) {
	  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
	    fifo_push(f, c);
	  }
	}
#endif

/*
static inline unsigned char fifo_pop_locked(FIFOBuffer *f) {
  unsigned char c;
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    c = fifo_pop(f);
  }
  return c;
}
*/

inline void fifo_init(FIFOBuffer *f, unsigned char *buffer, size_t size) {
  f->head = f->tail = f->begin = buffer;
  f->end = buffer + size;
}

inline size_t fifo_len(FIFOBuffer *f) {
  return f->end - f->begin;
}

typedef struct FIFOBuffer16
{
  uint16_t *begin;
  uint16_t *end;
  uint16_t * volatile head;
  uint16_t * volatile tail;
} FIFOBuffer16;

inline bool fifo16_isempty(const FIFOBuffer16 *f) {
  return f->head == f->tail;
}

inline bool fifo16_isfull(const FIFOBuffer16 *f) {
  return ((f->head == f->begin) && (f->tail == f->end)) || (f->tail == f->head - 1);
}

inline void fifo16_push(FIFOBuffer16 *f, uint16_t c) {
  *(f->tail) = c;

  if (f->tail == f->end) {
    f->tail = f->begin;
  } else {
    f->tail++;
  }
}

inline uint16_t fifo16_pop(FIFOBuffer16 *f) {
  if(f->head == f->end) {
    f->head = f->begin;
    return *(f->end);
  } else {
    return *(f->head++);
  }
}

inline void fifo16_flush(FIFOBuffer16 *f) {
  f->head = f->tail;
}

#if MCU_VARIANT != MCU_ESP32
	static inline bool fifo16_isempty_locked(const FIFOBuffer16 *f) {
	  bool result;
	  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
	    result = fifo16_isempty(f);
	  }

	  return result;
	}
#endif

/*
static inline bool fifo16_isfull_locked(const FIFOBuffer16 *f) {
  bool result;
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    result = fifo16_isfull(f);
  }
  return result;
}


static inline void fifo16_push_locked(FIFOBuffer16 *f, uint16_t c) {
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    fifo16_push(f, c);
  }
}

static inline size_t fifo16_pop_locked(FIFOBuffer16 *f) {
  size_t c;
  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
    c = fifo16_pop(f);
  }
  return c;
}
*/

inline void fifo16_init(FIFOBuffer16 *f, uint16_t *buffer, uint16_t size) {
  f->head = f->tail = f->begin = buffer;
  f->end = buffer + size;
}

inline uint16_t fifo16_len(FIFOBuffer16 *f) {
  return (f->end - f->begin);
}