mask files

The mask files are generated for every FPGA tile type. They store the information which bits in the bitstream can configure the given tile type.

Naming convention

The naming scheme for the mask files is the following:


Note that auxiliary mask_<tile>.origin_info.db files provide additional information about the fuzzer, which produced the database file. This file is optional.

Every tile is configured at least by one of three configurational buses mentioned in the Configuration Section. The default bus is called CLB_IO_CLK. If the tile can also be configured by another bus, it has an additional mask_<tile>.<bus_name>.db related to that bus.

For example:

  • mask_dsp_r.db

  • mask_bram_l.db (configured with default CLB_IO_CLK bus)

  • mask_bram_l.block_ram.db (configured with BLOCK_RAM bus)

File format

The file consists of records that describe the configuration bits for the particular tile type. Each entry inside the file is of the form:

bit <frame_address_offset>_<bit_position>

This means that the tile can be configured by a bit located in the frame at the address <base_frame_addr> + <frame_address_offset>, at position <tile_offset> + <bit_position>. Information about <base_frame_address> and <tile_offset> can be taken from part specific tilegrid.json file.


Below there is a part of artix7 mask_clbll_l.db file describing a FPGA CLBLL tile:

bit 00_61
bit 00_62
bit 00_63
bit 01_00
bit 01_01
bit 01_02

The line bit 01_02 means that the CLBL_LL tile can be configured by the bit located in the frame at the address <base_frame_address> + 0x01, at position <tile_offset> + 0x2.

The tilegrid.json is a file specific to a given chip package. For xc7a35tcpg236-1 we can find an exemplary CLBLL_L entry:

"CLBLL_L_X2Y0": {
    "bits": {
        "CLB_IO_CLK": {
            "baseaddr": "0x00400100",
            "frames": 36,
            "offset": 0,
            "words": 2
    "clock_region": "X0Y0",
    "grid_x": 10,
    "grid_y": 155,
    "pin_functions": {},
    "sites": {
        "SLICE_X0Y0": "SLICEL",
        "SLICE_X1Y0": "SLICEL"
    "type": "CLBLL_L"

The <base_frame_addr> can be found as a argument of the “baseaddr” key and for CLBLL_L_X2Y0 tile it is equal to 0x00400100. The <tile_offset> on the other hand is an argument of the “offset” key. Here it is equal to 0.

Finally, we are able to compute the bit location associated with the bit 01_02 entry.

The configuration bit for this record can be found in the following frame address:

0x00400100 + 0x01 = 0x00400101

Located at the bit position:

0x0 + 0x2 = 0x2

More about the configuration process and the meaning of the frame can be found in the Configuration Section.