Analysis of the Header Information in Xilinx FPGA Bitstream Files

Xilinx FPGA configuration files, in .bit and .bin formats, are binary configuration data files. The .bit file includes header information that is not required to be programmed into the FPGA. In some loading or remote update scenarios, both types of configuration files can be used, but using the .bit file provides additional information. The length of the bitstream header is not fixed and depends on internal fields. From the header information, one can obtain the design name, FPGA model, compilation time, and the byte size of the configuration file.

Analysis of the Header Information in Xilinx FPGA Bitstream Files

Analysis of the Header Information in Xilinx FPGA Bitstream Files

Attached is the code for processing the bit file header information in U-Boot.

int fpga_loadbitstream(int devnum, char *fpgadata, size_t size, bitstream_type bstype){    unsigned int length;    unsigned int swapsize;    unsigned char *dataptr;    unsigned int i;    const fpga_desc *desc;    xilinx_desc *xdesc;     dataptr = (unsigned char *)fpgadata;    /* Find out fpga_description */    desc = fpga_validate(devnum, dataptr, 0, (char *)__func__);    /* Assign xilinx device description */    xdesc = desc->devdesc;    /* skip the first bytes of the bitsteam, their meaning is unknown */    length = (*dataptr << 8) + *(dataptr + 1);    dataptr += 2;    dataptr += length;    /* get design name (identifier, length, string) */    length = (*dataptr << 8) + *(dataptr + 1);    dataptr += 2;    if (*dataptr++ != 0x61) {        debug("%s: Design name id not recognized in bitstream\n", __func__);        return FPGA_FAIL;    }    length = (*dataptr << 8) + *(dataptr + 1);    dataptr += 2;    printf("  design filename = \"%s\"\n", dataptr);    dataptr += length;    /* get part number (identifier, length, string) */    if (*dataptr++ != 0x62) {        printf("%s: Part number id not recognized in bitstream\n", __func__);        return FPGA_FAIL;    }    length = (*dataptr << 8) + *(dataptr + 1);    dataptr += 2;    if (xdesc->name) {        i = (ulong)strstr((char *)dataptr, xdesc->name);        if (!i) {            printf("%s: Wrong bitstream ID for this device\n", __func__);            printf("%s: Bitstream ID %s, current device ID %d/%s\n",                   __func__, dataptr, devnum, xdesc->name);            return FPGA_FAIL;        }    } else {        printf("%s: Please fill correct device ID to xilinx_desc\n", __func__);    }    printf("  part number = \"%s\"\n", dataptr);    dataptr += length;    /* get date (identifier, length, string) */    if (*dataptr++ != 0x63) {        printf("%s: Date identifier not recognized in bitstream\n", __func__);        return FPGA_FAIL;    }    length = (*dataptr << 8) + *(dataptr+1);    dataptr += 2;    printf("  date = \"%s\"\n", dataptr);    dataptr += length;    /* get time (identifier, length, string) */    if (*dataptr++ != 0x64) {        printf("%s: Time identifier not recognized in bitstream\n", __func__);        return FPGA_FAIL;    }    length = (*dataptr << 8) + *(dataptr+1);    dataptr += 2;    printf("  time = \"%s\"\n", dataptr);    dataptr += length;    /* get fpga data length (identifier, length) */    if (*dataptr++ != 0x65) {        printf("%s: Data length id not recognized in bitstream\n", __func__);        return FPGA_FAIL;    }    swapsize = ((unsigned int) *dataptr << 24) +             ((unsigned int) *(dataptr + 1) << 16) +             ((unsigned int) *(dataptr + 2) << 8) +             ((unsigned int) *(dataptr + 3));    dataptr += 4;    printf("  bytes in bitstream = %d\n", swapsize);    return fpga_load(devnum, dataptr, swapsize, bstype, 0);}

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