DCD Overview

The main functionality of the tool is to generate the Device Configuration Data (DCD) image using the format and constraints specified in the Boot ROM reference manual.

Upon reset, all peripheral registers in the system have their default values. However, these settings typically are not ideal for achieving optimal system performance. Moreover, there are some peripherals that must be configured before they can even be used. DCD is the configuration information contained in the DCD Image, that the Boot ROM interprets to configure various peripherals on the device. The Boot ROM determines the location of the DCD table by the pointer in the Image Vector Table.

The DCD data is comprised of the following three type of commands:

  • Write Data command:

    • The Write Data command is used to write a list of given 1-byte, 2-byte, or 4-byte values (or bitmasks) to a corresponding list of target addresses. The format of Write Data commands is a big-endian byte array.

    • The command's target width refers to its value size (1, 2 or 4 bytes).

    • The address must be a multiple of the target width.

    • The command's action can be one of the following:

      Action Interpretation
      *address = val_mask Write value
      *address &= ~val_mask Clear bitmask
      *address |= val_mask Set bitmask
  • Check Data command:

    • The Check Data command is used to test for a given 1, 2, or 4-byte bitmasks from a source address. The format of a Check data command is a big endian byte array.

    • The command's target width refers to its value size (1, 2 or 4 bytes).

    • The address must be a multiple of the target width.

    • The command's action can be one of the following:

      Action Interpretation
      (*address & mask) == 0 All bits in mask are clear
      (*address & mask) == mask All bits in mask are set
      (*address & mask) != mask At least one bit in mask is clear
      (*address & mask) != 0 At least one bit in mask set
  • Nop Command:

    • This command has no effect. The format of NOP Command is a big endian 4-byte array.