5.

TCG TPM Command Data Bytes Transfer Format

5.1

TCG TPM Command Protocol

The TPM command protocol, as defined by the TCG TPM specification, specifies an initial predefined

sequence of 10 data bytes for all commands transmitted to the TPM and also for all responses returned

by the TPM. A required component of this 10-byte sequence is commandSize, which specifies the total

number of data bytes in the command input or the response output.

The TPM uses a combination of commandSize and the master deasserting SPI_CS# inactive high to

define the termination point of all input and output sequences. After the input or output sequence has

completed, the TPM will automatically enter an Idle (Wait) state until the next communication is received

from the master. A new input or output sequence is initiated by the master asserting SPI_CS# active-low.

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 Master will continue 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>

5.3

TCG Command - Outgoing Operands and Sizes

The TPM will respond to every TCG command with 10 initial bytes that contain information common to all

commands:

•

tag (two bytes) — Specifies the authorization session type for the command.

•

responseSize (four bytes) — Total number of output bytes including tag and responseSize.

•

responseCode (four bytes) — The return code of the operation.

Following the 10-byte preamble, the TPM will continue to output data until the total number of data bytes

reaches responseSize. Depending on the command, zero bytes of data are possible. After output of the

final data byte and the master writing Command_Ready to a one, the TPM will enter an Idle state until the

next valid SPI command sequence is initiated by the master.

ATTPM20P

TCG TPM Command Data Bytes Transfer Format

Datasheet Summary

DS40002082A-page 10