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wolfTPM Hardware Interface Abstraction Layer (HAL) IO

A single HAL callback must be registered to handle communication to the hardware.

We distribute examples for several platforms to help with initial setup.

If using one of the builtin system provided hardware interfaces then NULL can be supplied for the HAL IO callback.

The available system TPM interfaces are:

  • Linux /dev/tpm0: Enabled with WOLFTPM_LINUX_DEV or --enable-devtpm.
  • Windows TBS: Enabled with WOLFTPM_WINAPI or --enable-winapi.
  • Software TPM Simulator: Enabled with WOLFTPM_SWTPM or --enable-swtpm.

If using a HAL IO callback it is registered on library initialization using:

  • TPM2 Native API's: TPM2_Init
  • wolfTPM Wrappers: wolfTPM2_Init

Example HAL Implementations

Platform Example File Build Option
Atmel ASF tpm_io_atmel.c WOLFSSL_ATMEL
Barebox tpm_io_barebox.c __BAREBOX__
Infineon tpm_io_infineon.c WOLFTPM_INFINEON_TRICORE
Linux tpm_io_linux.c __linux__
Microchip tpm_io_microchip.c WOLFTPM_MICROCHIP_HARMONY
QNX tpm_io_qnx.c __QNX__
ST Cube HAL tpm_io_st.c WOLFSSL_STM32_CUBEMX
Xilinx tpm_io_xilinx.c __XILINX__

HAL IO Callback Function

Here are the prototypes for the HAL callback function:

#ifdef WOLFTPM_ADV_IO
typedef int (*TPM2HalIoCb)(struct TPM2_CTX*, INT32 isRead, UINT32 addr,
    BYTE* xferBuf, UINT16 xferSz, void* userCtx);
#else
typedef int (*TPM2HalIoCb)(struct TPM2_CTX*, const BYTE* txBuf, BYTE* rxBuf,
    UINT16 xferSz, void* userCtx);
#endif

Here are example function definitions:

#ifdef WOLFTPM_ADV_IO
int TPM2_IoCb(TPM2_CTX*, int isRead, word32 addr, byte* buf, word16 size,
    void* userCtx);
#else
int TPM2_IoCb(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
    word16 xferSz, void* userCtx);
#endif

Additional Build options

  • WOLFTPM_CHECK_WAIT_STATE: Enables check of the wait state during a SPI transaction. Most TPM 2.0 chips require this and typically only require 0-2 wait cycles depending on the command. Only the Infineon TPM's guarantee no wait states.
  • WOLFTPM_ADV_IO: Enables advanced IO callback mode that includes TIS register and read/write flag. This is requires for I2C, but can be used with SPI also.
  • WOLFTPM_DEBUG_IO: Enable logging of the IO (if using the example HAL).

Additional Compiler macros

  • TPM2_SPI_DEV_PATH: Set to the device string to be opened by the Linux IOCb. Default: "/dev/spidev0."
  • TPM2_SPI_DEV_CS: Set to the number string of the CS to use. Default: "0"

These can be set during configure as: ./configure CPPFLAGS="-DTPM2_SPI_DEV_PATH="/dev/spidev0." -DTPM2_SPI_DEV_CS="0" "

Note that autodetect will use TPM2_SPI_DEV_PATH[0..4] for the searched device paths.