Software-based floppy disc data separator

/** * This is a software implementation of Jim Thompson's Phase-Jerked Loop * design, available from AnalogInnovations.com as the PDF file * "FloppyDataExtractor.pdf". * * This consists of: * A data synchroniser which forces RD_DATA to be active for 2 clock cycles. * A counter which increments constantly while the PLL is running, and is * reset to zero on an incoming data bit. * Whenever the counter reaches half of its maximum value, a * new data window is started. */ // Nanoseconds counters. Increment once per loop or "virtual" nanosecond unsigned long nsecs1 = 0, nsecs2=0; // Number of nanoseconds per acq tick -- (1/freq)*1e9. This is valid for 40MHz. const unsigned long NSECS_PER_ACQ = 25; // Number of nanoseconds per PLLCK tick -- (1/16e6)*1e9. 16MHz. // This should be the reciprocal of 32 times the data rate in kbps, multiplied // by 1e9 to get the time in nanoseconds. const unsigned long NSECS_PER_PLLCK = 125/2; // Number of clock increments per loop (timing granularity) const unsigned long TIMER_INCREMENT = 1; // Maximum value of the PJL counter. Determines the granularity of phase changes. const unsigned char PJL_COUNTER_MAX = 16; // Iterator for data buffer size_t i = 0; // True if RD_DATA was high in this clock cycle bool rd_latch = false; // Same but only active for 2Tcy (SHAPED_DATA) int shaped_data = 0; // Phase Jerked Loop counter unsigned char pjl_shifter = 0; // data window unsigned char data_window = 0; #ifdef VCD FILE *vcd = fopen("values.vcd", "wt"); fprintf(vcd, "$version DiscFerret Analyser D2/DPLL 0.1 $end\n" "$timescale 1 ns $end\n" "$var reg 1 * clock $end\n" "$var reg 1 ' pll_clock $end\n" "$var reg 1 ! rd_data $end\n" "$var reg 1 %% rd_data_latched $end\n" "$var reg 1 ^ shaped_data $end\n" "$var reg 8 & pjl_shifter $end\n" "$var reg 1 ( data_window $end\n" "$upscope $end\n" "$enddefinitions $end\n" "$dumpall\n" "0*\n" "0'\n" "0!\n" "0%%\n" "0^\n" "b00000000 &\n" "0(\n" "$end\n" ); #endif do { // Increment counters nsecs1 += TIMER_INCREMENT; nsecs2 += TIMER_INCREMENT; // Loop 1 -- floppy disc read channel if (nsecs1 >= (buf[i] * NSECS_PER_ACQ)) { // Flux transition. Set the read latches. rd_latch = true; shaped_data = 2; // Update nanoseconds counter for read channel, retain error factor nsecs1 -= (buf[i] * NSECS_PER_ACQ); // Update buffer position i++; } // Loop 2 -- DPLL channel if (nsecs2 >= NSECS_PER_PLLCK) { // Update nanoseconds counter for PLL, retain error factor nsecs2 -= NSECS_PER_PLLCK; // PJL loop if (shaped_data > 0) { pjl_shifter = 0; } else { // increment shifter pjl_shifter = (pjl_shifter + 1) % PJL_COUNTER_MAX; } // DWIN detect if (pjl_shifter == (PJL_COUNTER_MAX / 2)) { // Data window toggle. Latch the current RD_LATCH blob into the output buffer. mfmbits.push_back(rd_latch); // Clear the data latch ready for the next data window. rd_latch = false; // Update DWIN data_window ^= 0x01; } // Update shaped-data time counter if (shaped_data > 0) shaped_data--; } } while (i < buflen); printf("mfmbits count = %lu\n", mfmbits.size());