Bitstream formatΒΆ


Expand on rough notes

  • Specific byte pattern at beginning of file to allow hardware to determine width of bus providing configuration data.
  • Rest of file is 32-bit big-endian words
  • All data before 32-bit synchronization word (0xAA995566) is ignored by configuration state machine
  • Packetized format used to perform register reads/writes
    • Three packet header types
      • Type 0 packets exist only when performing zero-fill between rows
      • Type 1 used for writes up to 4096 words
      • Type 2 expands word count field to 27 bits by omitting register address
      • Type 2 must always be proceeded by Type 1 which sets register address
    • NOP packets are used for inserting required delays
    • Most registers only accept 1 word of data
    • Allowed register operations depends on interface used to send packets
      • Writing LOUT via JTAG is treated as a bad command
      • Single-frame FDRI writes via JTAG fail
  • CRC
    • Calculated automatically from writes: register address and data written
    • Expected value is written to CRC register
    • If there is a mismatch, error is flagged in status register
    • Writes to CRC register can be safely removed from a bitstream
    • Alternatively, replace with write to command register to reset calculated CRC value
  • Xilinx BIT header