MicroAPRS/Modem/protocol/mp1.h

#ifndef PROTOCOL_MP1
#define PROTOCOL_MP1

#include <cfg/compiler.h>
#include <io/kfile.h>

// Options
#define MP1_ENABLE_TCP_COMPATIBILITY false
#if MP1_ENABLE_TCP_COMPATIBILITY
    #define MP1_ENABLE_COMPRESSION false
    #define MP1_ENABLE_CSMA true
#else
    #define MP1_ENABLE_COMPRESSION true
    #define MP1_ENABLE_CSMA false
#endif

// Frame sizing & checksum
#define MP1_INTERLEAVE_SIZE 12
#if MP1_ENABLE_COMPRESSION
    #define MP1_MAX_FRAME_LENGTH 22 * MP1_INTERLEAVE_SIZE
    #define MP1_USE_TX_QUEUE false
#else
    #define MP1_MAX_FRAME_LENGTH 25 * MP1_INTERLEAVE_SIZE
    #define MP1_USE_TX_QUEUE true
    #define MP1_TX_QUEUE_LENGTH 2
    #define MP1_QUEUE_TX_WAIT 16UL
#endif
#define MP1_HEADER_SIZE 1
#define MP1_CHECKSUM_SIZE 1
#define MP1_MAX_DATA_SIZE MP1_MAX_FRAME_LENGTH - MP1_HEADER_SIZE - MP1_CHECKSUM_SIZE
#define MP1_MIN_FRAME_LENGTH MP1_INTERLEAVE_SIZE
#define MP1_DATA_BLOCK_SIZE ((MP1_INTERLEAVE_SIZE/3)*2)
#define MP1_CHECKSUM_INIT 0xAA

// These two parameters are used for 
// P-persistent CSMA
#define MP1_SETTLE_TIME 100UL	// The minimum wait time before even considering sending
#define MP1_SLOT_TIME 100UL     // The time to wait if deciding not to send
#define MP1_P_PERSISTENCE 85UL  // The probability (between 0 and 255) for sending
#define MP1_TXDELAY 0UL         // Delay between turning on the transmitter and sending

// We need to know some basic HDLC flag bytes
#define HDLC_FLAG  0x7E
#define HDLC_RESET 0x7F
#define AX25_ESC   0x1B

// We also define a few header flags and what
// to send as padding if we need to pad a
// packet. Due to forward error correction,
// packets must have an even number of bytes.
#define MP1_PADDING             0x55
#define MP1_HEADER_PADDED       0x01
#define MP1_HEADER_COMPRESSION  0x02

// Just a forward declaration that this struct exists
struct MP1Packet;

// The type of a callback function for passing
// back a decoded packet
typedef void (*mp1_callback_t)(struct MP1Packet *packet);

// Struct for a protocol context
typedef struct MP1 {
    uint8_t buffer[MP1_MAX_FRAME_LENGTH+MP1_INTERLEAVE_SIZE]; // A buffer for incoming packets
    KFile *modem;                                   // KFile access to the modem
    size_t packetLength;                            // Counter for received packet length
    size_t readLength;                              // This is the full read length, including parity bytes
    uint8_t calculatedParity;                       // Calculated parity for incoming data block
    mp1_callback_t callback;                        // The function to call when a packet has been received
    uint8_t checksum_in;                            // Rolling checksum for incoming packets
    uint8_t checksum_out;                           // Rolling checksum for outgoing packets
    bool reading;                                   // True when we have seen a HDLC flag
    bool escape;                                    // We need to know if we are in an escape sequence
    ticks_t settleTimer;                            // Timer used for carrier sense settling
    long correctionsMade;                           // A counter for how many corrections were made to a packet
    uint8_t interleaveCounter;                      // Keeps track of when we have received an entire interleaved block
    uint8_t interleaveOut[MP1_INTERLEAVE_SIZE];     // A buffer for interleaving bytes before they are sent
    uint8_t interleaveIn[MP1_INTERLEAVE_SIZE];      // A buffer for storing interleaved bytes before they are deinterleaved
    uint8_t randomSeed;                             // A seed for the pseudo-random number generator
    #if MP1_USE_TX_QUEUE
        bool queueProcessing;                       // For sending queued frames without preamble after first one
        size_t queueLength;                         // The length of the transmission queue
        size_t frameLengths[MP1_TX_QUEUE_LENGTH];   // The lengths of the frames in the queue
        uint8_t frameQueue[MP1_TX_QUEUE_LENGTH]     // A buffer for a queued frame
                              [MP1_MAX_DATA_SIZE];
    #endif
} MP1;

// A struct encapsulating a network packet
typedef struct MP1Packet {
    const uint8_t *data;		// Pointer to the actual data in the packet
    size_t dataLength;          // The length of the received data
} MP1Packet;

// Declarations of functions
void mp1Init(MP1 *mp1, KFile *modem, mp1_callback_t callback);
void mp1Read(MP1 *mp1, int byte);
void mp1Poll(MP1 *mp1);
void mp1Send(MP1 *mp1, void *_buffer, size_t length);
void mp1QueueFrame(MP1 *mp1, void *_buffer, size_t length);
void mp1ProcessQueue(MP1 *mp1);
bool mp1CarrierSense(MP1 *mp1);

int freeRam(void);
size_t compress(uint8_t *input, size_t length);
size_t decompress(uint8_t *input, size_t length);
void mp1Deinterleave(MP1 *mp1);
void mp1Interleave(MP1 *mp1, uint8_t byte);

#endif