5.2 TCG Command - Incoming Operands and Sizes

Every TCG command begins with 10 initial bytes that contain information common to all commands:

  • tag (two bytes) — Specifies the authorization session type for the command
  • commandSize (four bytes) — Total number of input bytes including tag and commandSize
  • commandCode (four bytes) — Command code as defined in TCG TPM specification

Following the 10-byte preamble, the SPI host continues to transmit the remaining command data bytes as specified by the TCG TPM specification until the total number of bytes reaches commandSize.

Table 5-1. Command Data Written to the TPM
tag[0]tag[1]

commandSize[0]commandSize[1]commandSize[2]commandSize[3]

commandCode[0]commandCode[1]commandCode[2]commandCode[3]