satdump/plugins/goes_support/goes/sd/sd_deframer.cpp

#include "sd_deframer.h"
#include <cstdint>
#include <cstring>

namespace goes
{
    namespace sd
    {
        GOESN_SD_Deframer::GOESN_SD_Deframer(int cadu_size) : FRM_SIZE(cadu_size)
        {
            frame_buffer = new uint8_t[FRM_SIZE];
        }

        GOESN_SD_Deframer::~GOESN_SD_Deframer()
        {
            delete[] frame_buffer;
        }

        int GOESN_SD_Deframer::getState()
        {
            return d_state;
        }

        int GOESN_SD_Deframer::work(uint8_t *input, int size, uint8_t *output)
        {
            int frame_count = 0;

            for (int ibit = 0; ibit < size; ibit++) // We work bit-per-bit
            {
                shifter = (shifter << 1 | input[ibit]) & 0b11111111111111;

                if (in_frame)
                {
                    write_bit(input[ibit]);

                    if (bit_of_frame == FRM_SIZE) // Write frame out
                    {
                        memcpy(&output[frame_count * (FRM_SIZE / 8)], frame_buffer, FRM_SIZE / 8);
                        frame_count++;
                    }
                    else if (bit_of_frame == FRM_SIZE + FRM_ASM_SIZE - 1) // Skip to the next ASM
                    {
                        in_frame = false;
                    }

                    continue;
                }

                if (d_state == STATE_NOSYNC)
                {
                    if (shifter == FRM_ASM)
                    {
                        reset_frame();
                        in_frame = true;
                        d_state = STATE_SYNCING;
                        d_good_asm = d_invalid_asm = 0;
                    }
                }
                else if (d_state == STATE_SYNCING)
                {
                    if (compare_16(shifter, FRM_ASM) < d_state)
                    {
                        reset_frame();
                        in_frame = true;
                        d_invalid_asm = 0;
                        d_good_asm++;

                        if (d_good_asm > 10)
                            d_state = STATE_SYNCED;
                    }
                    else
                    {
                        d_invalid_asm++;
                        d_good_asm = 0;

                        if (d_invalid_asm > 2)
                        {
                            d_state = STATE_NOSYNC;
                        }
                    }
                }
                else if (d_state == STATE_SYNCED)
                {
                    if (compare_16(shifter, FRM_ASM) < d_state)
                    {
                        reset_frame();
                        in_frame = true;
                    }
                    else
                    {
                        d_good_asm = d_invalid_asm = 0;
                        d_state = STATE_NOSYNC; // Reset to hard NOSYNC, so we correct for a possible new inversion state
                    }
                }
            }

            return frame_count;
        }

        void GOESN_SD_Deframer::write_bit(uint8_t b)
        {
            frame_buffer[bit_of_frame / 8] = frame_buffer[bit_of_frame / 8] << 1 | b;
            bit_of_frame++;
        }

        void GOESN_SD_Deframer::reset_frame()
        {
            memset(frame_buffer, 0, FRM_SIZE / 8);
            bit_of_frame = 0;
            for (int i = 13; i >= 0; i--)
                write_bit((FRM_ASM >> i) & 1);
        }
    }
}