apdu works.

[proxmark3-svn] / armsrc / fpgaloader.c

//-----------------------------------------------------------------------------
// Jonathan Westhues, April 2006
// iZsh <izsh at fail0verflow.com>, 2014
//
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Routines to load the FPGA image, and then to configure the FPGA's major
// mode once it is configured.
//-----------------------------------------------------------------------------

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>
#include "fpgaloader.h"
#include "proxmark3.h"
#include "util.h"
#include "string.h"
#include "BigBuf.h"
#include "zlib.h"

extern void Dbprintf(const char *fmt, ...);

// remember which version of the bitstream we have already downloaded to the FPGA
static int downloaded_bitstream = FPGA_BITSTREAM_ERR;

// this is where the bitstreams are located in memory:
extern uint8_t _binary_obj_fpga_all_bit_z_start, _binary_obj_fpga_all_bit_z_end;

static uint8_t *fpga_image_ptr = NULL;
static uint32_t uncompressed_bytes_cnt;

static const uint8_t _bitparse_fixed_header[] = {0x00, 0x09, 0x0f, 0xf0, 0x0f, 0xf0, 0x0f, 0xf0, 0x0f, 0xf0, 0x00, 0x00, 0x01};
#define FPGA_BITSTREAM_FIXED_HEADER_SIZE        sizeof(_bitparse_fixed_header)
#define OUTPUT_BUFFER_LEN               80
#define FPGA_INTERLEAVE_SIZE    288

//-----------------------------------------------------------------------------
// Set up the Serial Peripheral Interface as master
// Used to write the FPGA config word
// May also be used to write to other SPI attached devices like an LCD
//-----------------------------------------------------------------------------
void SetupSpi(int mode)
{
        // PA10 -> SPI_NCS2 chip select (LCD)
        // PA11 -> SPI_NCS0 chip select (FPGA)
        // PA12 -> SPI_MISO Master-In Slave-Out
        // PA13 -> SPI_MOSI Master-Out Slave-In
        // PA14 -> SPI_SPCK Serial Clock

        // Disable PIO control of the following pins, allows use by the SPI peripheral
        AT91C_BASE_PIOA->PIO_PDR =
                GPIO_NCS0       |
                GPIO_NCS2       |
                GPIO_MISO       |
                GPIO_MOSI       |
                GPIO_SPCK;

        AT91C_BASE_PIOA->PIO_ASR =
                GPIO_NCS0       |
                GPIO_MISO       |
                GPIO_MOSI       |
                GPIO_SPCK;

        AT91C_BASE_PIOA->PIO_BSR = GPIO_NCS2;

        //enable the SPI Peripheral clock
        AT91C_BASE_PMC->PMC_PCER = (1<<AT91C_ID_SPI);
        // Enable SPI
        AT91C_BASE_SPI->SPI_CR = AT91C_SPI_SPIEN;

        switch (mode) {
                case SPI_FPGA_MODE:
                        AT91C_BASE_SPI->SPI_MR =
                                ( 0 << 24)      |       // Delay between chip selects (take default: 6 MCK periods)
                                (14 << 16)      |       // Peripheral Chip Select (selects FPGA SPI_NCS0 or PA11)
                                ( 0 << 7)       |       // Local Loopback Disabled
                                ( 1 << 4)       |       // Mode Fault Detection disabled
                                ( 0 << 2)       |       // Chip selects connected directly to peripheral
                                ( 0 << 1)       |       // Fixed Peripheral Select
                                ( 1 << 0);              // Master Mode
                        AT91C_BASE_SPI->SPI_CSR[0] =
                                ( 1 << 24)      |       // Delay between Consecutive Transfers (32 MCK periods)
                                ( 1 << 16)      |       // Delay Before SPCK (1 MCK period)
                                ( 6 << 8)       |       // Serial Clock Baud Rate (baudrate = MCK/6 = 24Mhz/6 = 4M baud
                                ( 8 << 4)       |       // Bits per Transfer (16 bits)
                                ( 0 << 3)       |       // Chip Select inactive after transfer
                                ( 1 << 1)       |       // Clock Phase data captured on leading edge, changes on following edge
                                ( 0 << 0);              // Clock Polarity inactive state is logic 0
                        break;
                case SPI_LCD_MODE:
                        AT91C_BASE_SPI->SPI_MR =
                                ( 0 << 24)      |       // Delay between chip selects (take default: 6 MCK periods)
                                (11 << 16)      |       // Peripheral Chip Select (selects LCD SPI_NCS2 or PA10)
                                ( 0 << 7)       |       // Local Loopback Disabled
                                ( 1 << 4)       |       // Mode Fault Detection disabled
                                ( 0 << 2)       |       // Chip selects connected directly to peripheral
                                ( 0 << 1)       |       // Fixed Peripheral Select
                                ( 1 << 0);              // Master Mode
                        AT91C_BASE_SPI->SPI_CSR[2] =
                                ( 1 << 24)      |       // Delay between Consecutive Transfers (32 MCK periods)
                                ( 1 << 16)      |       // Delay Before SPCK (1 MCK period)
                                ( 6 << 8)       |       // Serial Clock Baud Rate (baudrate = MCK/6 = 24Mhz/6 = 4M baud
                                ( 1 << 4)       |       // Bits per Transfer (9 bits)
                                ( 0 << 3)       |       // Chip Select inactive after transfer
                                ( 1 << 1)       |       // Clock Phase data captured on leading edge, changes on following edge
                                ( 0 << 0);              // Clock Polarity inactive state is logic 0
                        break;
                default:                                // Disable SPI
                        AT91C_BASE_SPI->SPI_CR = AT91C_SPI_SPIDIS;
                        break;
        }
}

//-----------------------------------------------------------------------------
// Set up the synchronous serial port, with the one set of options that we
// always use when we are talking to the FPGA. Both RX and TX are enabled.
//-----------------------------------------------------------------------------
void FpgaSetupSsc(void)
{
        // First configure the GPIOs, and get ourselves a clock.
        AT91C_BASE_PIOA->PIO_ASR =
                GPIO_SSC_FRAME  |
                GPIO_SSC_DIN    |
                GPIO_SSC_DOUT   |
                GPIO_SSC_CLK;
        AT91C_BASE_PIOA->PIO_PDR = GPIO_SSC_DOUT;

        AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_SSC);

        // Now set up the SSC proper, starting from a known state.
        AT91C_BASE_SSC->SSC_CR = AT91C_SSC_SWRST;

        // RX clock comes from TX clock, RX starts when TX starts, data changes
        // on RX clock rising edge, sampled on falling edge
        AT91C_BASE_SSC->SSC_RCMR = SSC_CLOCK_MODE_SELECT(1) | SSC_CLOCK_MODE_START(1);

        // 8 bits per transfer, no loopback, MSB first, 1 transfer per sync
        // pulse, no output sync
        AT91C_BASE_SSC->SSC_RFMR = SSC_FRAME_MODE_BITS_IN_WORD(8) |     AT91C_SSC_MSBF | SSC_FRAME_MODE_WORDS_PER_TRANSFER(0);

        // clock comes from TK pin, no clock output, outputs change on falling
        // edge of TK, sample on rising edge of TK, start on positive-going edge of sync
        AT91C_BASE_SSC->SSC_TCMR = SSC_CLOCK_MODE_SELECT(2) |   SSC_CLOCK_MODE_START(5);

        // tx framing is the same as the rx framing
        AT91C_BASE_SSC->SSC_TFMR = AT91C_BASE_SSC->SSC_RFMR;

        AT91C_BASE_SSC->SSC_CR = AT91C_SSC_RXEN | AT91C_SSC_TXEN;
}

//-----------------------------------------------------------------------------
// Set up DMA to receive samples from the FPGA. We will use the PDC, with
// a single buffer as a circular buffer (so that we just chain back to
// ourselves, not to another buffer). The stuff to manipulate those buffers
// is in apps.h, because it should be inlined, for speed.
//-----------------------------------------------------------------------------
bool FpgaSetupSscDma(uint8_t *buf, int len)
{
        if (buf == NULL) return false;

        AT91C_BASE_PDC_SSC->PDC_PTCR = AT91C_PDC_RXTDIS;        // Disable DMA Transfer
        AT91C_BASE_PDC_SSC->PDC_RPR = (uint32_t) buf;           // transfer to this memory address
        AT91C_BASE_PDC_SSC->PDC_RCR = len;                                      // transfer this many bytes
        AT91C_BASE_PDC_SSC->PDC_RNPR = (uint32_t) buf;          // next transfer to same memory address
        AT91C_BASE_PDC_SSC->PDC_RNCR = len;                                     // ... with same number of bytes
        AT91C_BASE_PDC_SSC->PDC_PTCR = AT91C_PDC_RXTEN;         // go!

        return true;
}


//----------------------------------------------------------------------------
// Uncompress (inflate) the FPGA data. Returns one decompressed byte with
// each call. 
//----------------------------------------------------------------------------
static int get_from_fpga_combined_stream(z_streamp compressed_fpga_stream, uint8_t *output_buffer)
{
        if (fpga_image_ptr == compressed_fpga_stream->next_out) {       // need more data
                compressed_fpga_stream->next_out = output_buffer;
                compressed_fpga_stream->avail_out = OUTPUT_BUFFER_LEN;
                fpga_image_ptr = output_buffer;
                int res = inflate(compressed_fpga_stream, Z_SYNC_FLUSH);
                if (res != Z_OK)
                        Dbprintf("inflate returned: %d, %s", res, compressed_fpga_stream->msg);

                if (res < 0)
                        return res;
        }

        uncompressed_bytes_cnt++;
        
        return *fpga_image_ptr++;
}

//----------------------------------------------------------------------------
// Undo the interleaving of several FPGA config files. FPGA config files
// are combined into one big file:
// 288 bytes from FPGA file 1, followed by 288 bytes from FGPA file 2, etc.
//----------------------------------------------------------------------------
static int get_from_fpga_stream(int bitstream_version, z_streamp compressed_fpga_stream, uint8_t *output_buffer)
{
        while((uncompressed_bytes_cnt / FPGA_INTERLEAVE_SIZE) % FPGA_BITSTREAM_MAX != (bitstream_version - 1)) {
                // skip undesired data belonging to other bitstream_versions
                get_from_fpga_combined_stream(compressed_fpga_stream, output_buffer);
        }

        return get_from_fpga_combined_stream(compressed_fpga_stream, output_buffer);
        
}


static voidpf fpga_inflate_malloc(voidpf opaque, uInt items, uInt size)
{
        return BigBuf_malloc(items*size);
}


static void fpga_inflate_free(voidpf opaque, voidpf address)
{
        BigBuf_free(); BigBuf_Clear_ext(false);
}


//----------------------------------------------------------------------------
// Initialize decompression of the respective (HF or LF) FPGA stream 
//----------------------------------------------------------------------------
static bool reset_fpga_stream(int bitstream_version, z_streamp compressed_fpga_stream, uint8_t *output_buffer)
{
        uint8_t header[FPGA_BITSTREAM_FIXED_HEADER_SIZE];
        
        uncompressed_bytes_cnt = 0;
        
        // initialize z_stream structure for inflate:
        compressed_fpga_stream->next_in = &_binary_obj_fpga_all_bit_z_start;
        compressed_fpga_stream->avail_in = &_binary_obj_fpga_all_bit_z_start - &_binary_obj_fpga_all_bit_z_end;
        compressed_fpga_stream->next_out = output_buffer;
        compressed_fpga_stream->avail_out = OUTPUT_BUFFER_LEN;
        compressed_fpga_stream->zalloc = &fpga_inflate_malloc;
        compressed_fpga_stream->zfree = &fpga_inflate_free;

        inflateInit2(compressed_fpga_stream, 0);

        fpga_image_ptr = output_buffer;

        for (uint16_t i = 0; i < FPGA_BITSTREAM_FIXED_HEADER_SIZE; i++) {
                header[i] = get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer);
        }
        
        // Check for a valid .bit file (starts with _bitparse_fixed_header)
        if(memcmp(_bitparse_fixed_header, header, FPGA_BITSTREAM_FIXED_HEADER_SIZE) == 0) {
                return true;
        } else {
                return false;
        }
}


static void DownloadFPGA_byte(unsigned char w)
{
#define SEND_BIT(x) { if(w & (1<<x) ) HIGH(GPIO_FPGA_DIN); else LOW(GPIO_FPGA_DIN); HIGH(GPIO_FPGA_CCLK); LOW(GPIO_FPGA_CCLK); }
        SEND_BIT(7);
        SEND_BIT(6);
        SEND_BIT(5);
        SEND_BIT(4);
        SEND_BIT(3);
        SEND_BIT(2);
        SEND_BIT(1);
        SEND_BIT(0);
}

// Download the fpga image starting at current stream position with length FpgaImageLen bytes
static void DownloadFPGA(int bitstream_version, int FpgaImageLen, z_streamp compressed_fpga_stream, uint8_t *output_buffer)
{

        //Dbprintf("DownloadFPGA(len: %d)", FpgaImageLen);
        
        int i=0;

        AT91C_BASE_PIOA->PIO_OER = GPIO_FPGA_ON;
        AT91C_BASE_PIOA->PIO_PER = GPIO_FPGA_ON;
        HIGH(GPIO_FPGA_ON);             // ensure everything is powered on

        SpinDelay(50);

        LED_D_ON();

        // These pins are inputs
    AT91C_BASE_PIOA->PIO_ODR =
        GPIO_FPGA_NINIT |
        GPIO_FPGA_DONE;
        // PIO controls the following pins
    AT91C_BASE_PIOA->PIO_PER =
        GPIO_FPGA_NINIT |
        GPIO_FPGA_DONE;
        // Enable pull-ups
        AT91C_BASE_PIOA->PIO_PPUER =
                GPIO_FPGA_NINIT |
                GPIO_FPGA_DONE;

        // setup initial logic state
        HIGH(GPIO_FPGA_NPROGRAM);
        LOW(GPIO_FPGA_CCLK);
        LOW(GPIO_FPGA_DIN);
        // These pins are outputs
        AT91C_BASE_PIOA->PIO_OER =
                GPIO_FPGA_NPROGRAM      |
                GPIO_FPGA_CCLK          |
                GPIO_FPGA_DIN;

        // enter FPGA configuration mode
        LOW(GPIO_FPGA_NPROGRAM);
        SpinDelay(50);
        HIGH(GPIO_FPGA_NPROGRAM);

        i=100000;
        // wait for FPGA ready to accept data signal
        while ((i) && ( !(AT91C_BASE_PIOA->PIO_PDSR & GPIO_FPGA_NINIT ) ) ) {
                i--;
        }

        // crude error indicator, leave both red LEDs on and return
        if (i==0){
                LED_C_ON();
                LED_D_ON();
                return;
        }

        for(i = 0; i < FpgaImageLen; i++) {
                int b = get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer);
                if (b < 0) {
                        Dbprintf("Error %d during FpgaDownload", b);
                        break;
                }
                DownloadFPGA_byte(b);
        }
        
        // continue to clock FPGA until ready signal goes high
        i=100000;
        while ( (i--) && ( !(AT91C_BASE_PIOA->PIO_PDSR & GPIO_FPGA_DONE ) ) ) {
                HIGH(GPIO_FPGA_CCLK);
                LOW(GPIO_FPGA_CCLK);
        }
        // crude error indicator, leave both red LEDs on and return
        if (i==0){
                LED_C_ON();
                LED_D_ON();
                return;
        }
        LED_D_OFF();
}


/* Simple Xilinx .bit parser. The file starts with the fixed opaque byte sequence
 * 00 09 0f f0 0f f0 0f f0 0f f0 00 00 01
 * After that the format is 1 byte section type (ASCII character), 2 byte length
 * (big endian), <length> bytes content. Except for section 'e' which has 4 bytes
 * length.
 */
static int bitparse_find_section(int bitstream_version, char section_name, unsigned int *section_length, z_streamp compressed_fpga_stream, uint8_t *output_buffer)
{
        int result = 0;
        #define MAX_FPGA_BIT_STREAM_HEADER_SEARCH 100  // maximum number of bytes to search for the requested section
        uint16_t numbytes = 0;
        while(numbytes < MAX_FPGA_BIT_STREAM_HEADER_SEARCH) {
                char current_name = get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer);
                numbytes++;
                unsigned int current_length = 0;
                if(current_name < 'a' || current_name > 'e') {
                        /* Strange section name, abort */
                        break;
                }
                current_length = 0;
                switch(current_name) {
                case 'e':
                        /* Four byte length field */
                        current_length += get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer) << 24;
                        current_length += get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer) << 16;
                        numbytes += 2;
                default: /* Fall through, two byte length field */
                        current_length += get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer) << 8;
                        current_length += get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer) << 0;
                        numbytes += 2;
                }

                if(current_name != 'e' && current_length > 255) {
                        /* Maybe a parse error */
                        break;
                }

                if(current_name == section_name) {
                        /* Found it */
                        *section_length = current_length;
                        result = 1;
                        break;
                }

                for (uint16_t i = 0; i < current_length && numbytes < MAX_FPGA_BIT_STREAM_HEADER_SEARCH; i++) {
                        get_from_fpga_stream(bitstream_version, compressed_fpga_stream, output_buffer);
                        numbytes++;
                }
        }

        return result;
}


//----------------------------------------------------------------------------
// Check which FPGA image is currently loaded (if any). If necessary 
// decompress and load the correct (HF or LF) image to the FPGA
//----------------------------------------------------------------------------
void FpgaDownloadAndGo(int bitstream_version)
{
        z_stream compressed_fpga_stream;
        uint8_t output_buffer[OUTPUT_BUFFER_LEN] = {0x00};
        
        // check whether or not the bitstream is already loaded
        if (downloaded_bitstream == bitstream_version)
                return;

        // make sure that we have enough memory to decompress
        BigBuf_free(); BigBuf_Clear_ext(false); 
        
        if (!reset_fpga_stream(bitstream_version, &compressed_fpga_stream, output_buffer)) {
                return;
        }

        unsigned int bitstream_length;
        if(bitparse_find_section(bitstream_version, 'e', &bitstream_length, &compressed_fpga_stream, output_buffer)) {
                DownloadFPGA(bitstream_version, bitstream_length, &compressed_fpga_stream, output_buffer);
                downloaded_bitstream = bitstream_version;
        }

        inflateEnd(&compressed_fpga_stream);
        
        // free eventually allocated BigBuf memory
        BigBuf_free(); BigBuf_Clear_ext(false); 
}       


//-----------------------------------------------------------------------------
// Gather version information from FPGA image. Needs to decompress the begin 
// of the respective (HF or LF) image.
// Note: decompression makes use of (i.e. overwrites) BigBuf[]. It is therefore
// advisable to call this only once and store the results for later use.
//-----------------------------------------------------------------------------
void FpgaGatherVersion(int bitstream_version, char *dst, int len)
{
        unsigned int fpga_info_len;
        char tempstr[40] = {0x00};
        z_stream compressed_fpga_stream;
        uint8_t output_buffer[OUTPUT_BUFFER_LEN] = {0x00};
        
        dst[0] = '\0';

        // ensure that we can allocate enough memory for decompression:
        BigBuf_free(); BigBuf_Clear_ext(false);

        if (!reset_fpga_stream(bitstream_version, &compressed_fpga_stream, output_buffer))
                return;

        if(bitparse_find_section(bitstream_version, 'a', &fpga_info_len, &compressed_fpga_stream, output_buffer)) {
                for (uint16_t i = 0; i < fpga_info_len; i++) {
                        char c = (char)get_from_fpga_stream(bitstream_version, &compressed_fpga_stream, output_buffer);
                        if (i < sizeof(tempstr)) {
                                tempstr[i] = c;
                        }
                }
                if (!memcmp("fpga_lf", tempstr, 7))
                        strncat(dst, "LF ", len-1);
                else if (!memcmp("fpga_hf", tempstr, 7))
                        strncat(dst, "HF ", len-1);
        }
        strncat(dst, "FPGA image built", len-1);
        if(bitparse_find_section(bitstream_version, 'b', &fpga_info_len, &compressed_fpga_stream, output_buffer)) {
                strncat(dst, " for ", len-1);
                for (uint16_t i = 0; i < fpga_info_len; i++) {
                        char c = (char)get_from_fpga_stream(bitstream_version, &compressed_fpga_stream, output_buffer);
                        if (i < sizeof(tempstr)) {
                                tempstr[i] = c;
                        }
                }
                strncat(dst, tempstr, len-1);
        }
        if(bitparse_find_section(bitstream_version, 'c', &fpga_info_len, &compressed_fpga_stream, output_buffer)) {
                strncat(dst, " on ", len-1);
                for (uint16_t i = 0; i < fpga_info_len; i++) {
                        char c = (char)get_from_fpga_stream(bitstream_version, &compressed_fpga_stream, output_buffer);
                        if (i < sizeof(tempstr)) {
                                tempstr[i] = c;
                        }
                }
                strncat(dst, tempstr, len-1);
        }
        if(bitparse_find_section(bitstream_version, 'd', &fpga_info_len, &compressed_fpga_stream, output_buffer)) {
                strncat(dst, " at ", len-1);
                for (uint16_t i = 0; i < fpga_info_len; i++) {
                        char c = (char)get_from_fpga_stream(bitstream_version, &compressed_fpga_stream, output_buffer);
                        if (i < sizeof(tempstr)) {
                                tempstr[i] = c;
                        }
                }
                strncat(dst, tempstr, len-1);
        }
        
        strncat(dst, "\n", len-1);

        inflateEnd(&compressed_fpga_stream);
}


//-----------------------------------------------------------------------------
// Send a 16 bit command/data pair to the FPGA.
// The bit format is:  C3 C2 C1 C0 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
// where C is the 4 bit command and D is the 12 bit data
//-----------------------------------------------------------------------------
void FpgaSendCommand(uint16_t cmd, uint16_t v)
{
        SetupSpi(SPI_FPGA_MODE);
        while ((AT91C_BASE_SPI->SPI_SR & AT91C_SPI_TXEMPTY) == 0);              // wait for the transfer to complete
        AT91C_BASE_SPI->SPI_TDR = AT91C_SPI_LASTXFER | cmd | v;         // send the data
}
//-----------------------------------------------------------------------------
// Write the FPGA setup word (that determines what mode the logic is in, read
// vs. clone vs. etc.). This is now a special case of FpgaSendCommand() to
// avoid changing this function's occurence everywhere in the source code.
//-----------------------------------------------------------------------------
void FpgaWriteConfWord(uint8_t v)
{
        FpgaSendCommand(FPGA_CMD_SET_CONFREG, v);
}

//-----------------------------------------------------------------------------
// Set up the CMOS switches that mux the ADC: four switches, independently
// closable, but should only close one at a time. Not an FPGA thing, but
// the samples from the ADC always flow through the FPGA.
//-----------------------------------------------------------------------------
void SetAdcMuxFor(uint32_t whichGpio)
{
        AT91C_BASE_PIOA->PIO_OER =
                GPIO_MUXSEL_HIPKD |
                GPIO_MUXSEL_LOPKD |
                GPIO_MUXSEL_LORAW |
                GPIO_MUXSEL_HIRAW;

        AT91C_BASE_PIOA->PIO_PER =
                GPIO_MUXSEL_HIPKD |
                GPIO_MUXSEL_LOPKD |
                GPIO_MUXSEL_LORAW |
                GPIO_MUXSEL_HIRAW;

        LOW(GPIO_MUXSEL_HIPKD);
        LOW(GPIO_MUXSEL_HIRAW);
        LOW(GPIO_MUXSEL_LORAW);
        LOW(GPIO_MUXSEL_LOPKD);

        HIGH(whichGpio);
}

void Fpga_print_status(void) {
        Dbprintf("Fgpa");
        switch(downloaded_bitstream) {
                case FPGA_BITSTREAM_HF: Dbprintf("  mode....................HF"); break;
                case FPGA_BITSTREAM_LF: Dbprintf("  mode....................LF"); break;
                default:                Dbprintf("  mode....................%d", downloaded_bitstream); break;
        }
}

int FpgaGetCurrent() {
        return downloaded_bitstream;
}