diff --git a/CMakeLists.txt b/CMakeLists.txt
index b77a9df..b5e0c8e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -35,8 +35,10 @@ set(TPM_SOURCES
     src/tpm2_tis.c
     src/tpm2_winapi.c
     src/tpm2_wrap.c
+    hal/tpm_io.c
     )
 
+
 # default to build shared library
 option(BUILD_SHARED_LIBS "Build shared libraries (.dll/.so) instead of static ones (.lib/.a)" ON)
 add_library(wolftpm ${TPM_SOURCES})
@@ -157,7 +159,6 @@ endif()
 
 if (WOLFTPM_EXAMPLES)
     add_library(tpm_test_lib STATIC
-        examples/tpm_io.c
         examples/tpm_test_keys.c
         )
     target_link_libraries(tpm_test_lib wolftpm)
diff --git a/Makefile.am b/Makefile.am
index cd0a612..08716de 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -40,6 +40,7 @@ include certs/include.am
 include tests/include.am
 include docs/include.am
 include wrapper/include.am
+include hal/include.am
 
 EXTRA_DIST+= README.md
 EXTRA_DIST+= ChangeLog.md
diff --git a/README.md b/README.md
index 524c6d2..be9566c 100644
--- a/README.md
+++ b/README.md
@@ -70,13 +70,15 @@ Acronyms:
 
 The examples in this library are written for use on a Raspberry Pi and use the `spi_dev` interface.
 
-### IO Callback
+### IO Callback (HAL)
 
-For interfacing to your hardware platform see the example `examples/tpm_io.c` callback function `TPM2_IoCb`. Here you can modify or insert your own IO callback code for the TPM demo.
+See the HAL manual in [`hal/README.md] (hal/README.md).
 
-There are examples here for Linux, STM32 CubeMX, Atmel ASF, Xilinx, Infineon TriCore and BareBox.
+For interfacing to your hardware interface (SPI/I2C) a single HAL callback is used and configuration on initialization when calling `TPM2_Init` or `wolfTPM2_Init`.
 
-The advanced IO option (`--enable-advio`/`WOLFTPM_ADV_IO`) is required for I2C support because it adds the register and read/write flag as parameter to the IO callback.
+There are HAL examples in `hal` directory for Linux, STM32 CubeMX, Atmel ASF, Xilinx, Infineon TriCore and BareBox.
+
+We also support an advanced IO option (`--enable-advio`/`WOLFTPM_ADV_IO`), which adds the register and read/write flag as parameter to the IO callback. This is required for I2C support.
 
 ### Hardware
 
diff --git a/configure.ac b/configure.ac
index 1f6de94..02cc9f4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -387,6 +387,18 @@ then
 fi
 
 
+# Example HAL implementations
+AC_ARG_ENABLE([hal],
+    [AS_HELP_STRING([--enable-hal],[Enable example HAL interfaces (default: enabled)])],
+    [ ENABLED_EXAMPLE_HAL=$enableval ],
+    [ ENABLED_EXAMPLE_HAL=yes ]
+    )
+if test "x$ENABLED_EXAMPLE_HAL" = "xyes"
+then
+    AM_CFLAGS="$AM_CFLAGS -DWOLFTPM_EXAMPLE_HAL"
+fi
+
+
 # TIS / SPI Check Wait State support
 # Required for all but Infineon only
 if test "x$ENABLED_CHECKWAITSTATE" = "xyes" || test "x$ENABLED_AUTODETECT" = "xyes" || test "x$ENABLED_INFINEON" = "xno"
@@ -418,7 +430,7 @@ AM_CONDITIONAL([BUILD_WINAPI], [test "x$ENABLED_WINAPI" = "xyes"])
 AM_CONDITIONAL([BUILD_NUVOTON], [test "x$ENABLED_NUVOTON" = "xyes"])
 AM_CONDITIONAL([BUILD_CHECKWAITSTATE], [test "x$ENABLED_CHECKWAITSTATE" = "xyes"])
 AM_CONDITIONAL([BUILD_AUTODETECT], [test "x$ENABLED_AUTODETECT" = "xyes"])
-
+AM_CONDITIONAL([BUILD_HAL], [test "x$ENABLED_EXAMPLE_HAL" = "xyes"])
 
 
 CREATE_HEX_VERSION
diff --git a/docs/README.md b/docs/README.md
index 44055b8..7f8b8ca 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -66,7 +66,7 @@ For detailed build instructions see [/README.md](/README.md#building).
 
 The wolfTPM library has TPM 2.0 wrapper tests, native tests, and a sample benchmark application that come ready-to-use after a successful installation of wolfTPM. Below are some instructions on how to run the sample applications yourself.
 
-To interface with the hardware platform that is running these applications, please see the function "TPM2_IoCb" inside of examples/tpm_io.c.
+To interface with the hardware platform that is running these applications, please see the function `TPM2_IoCb` inside of `hal/tpm_io.c`.
 
 ### Examples
 
@@ -91,7 +91,7 @@ The general header files that should be included from wolfTPM is shown below:
 
 ### Example Design
 
-Every example application that is included with wolfTPM includes the `tpm_io.h` header file, located in `/examples`.
+Every example application that is included with wolfTPM includes the `tpm_io.h` header file, located in `/hal`.
 
 The `tpm_io.c` file sets up the example HAL IO callback necessary for testing and running the example applications with a Linux Kernel, STM32 CubeMX HAL or Atmel/Microchip ASF. The reference is easily modified, such that custom IO callbacks or different callbacks may be added or removed as desired.
 
diff --git a/examples/attestation/include.am b/examples/attestation/include.am
index 6d28907..ba7484f 100644
--- a/examples/attestation/include.am
+++ b/examples/attestation/include.am
@@ -8,13 +8,11 @@ noinst_PROGRAMS += examples/attestation/make_credential \
 noinst_HEADERS  += examples/attestation/credential.h
 
 examples_attestation_make_credential_SOURCES      = examples/attestation/make_credential.c \
-                                                    examples/tpm_io.c \
                                                     examples/tpm_test_keys.c
 examples_attestation_make_credential_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_attestation_make_credential_DEPENDENCIES = src/libwolftpm.la
 
 examples_attestation_activate_credential_SOURCES  = examples/attestation/activate_credential.c \
-                                                    examples/tpm_io.c \
                                                     examples/tpm_test_keys.c
 examples_attestation_activate_credential_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_attestation_activate_credential_DEPENDENCIES = src/libwolftpm.la
diff --git a/examples/bench/include.am b/examples/bench/include.am
index d762f27..eb7fca2 100644
--- a/examples/bench/include.am
+++ b/examples/bench/include.am
@@ -5,7 +5,6 @@ if BUILD_EXAMPLES
 noinst_PROGRAMS += examples/bench/bench
 noinst_HEADERS  += examples/bench/bench.h
 examples_bench_bench_SOURCES      = examples/bench/bench.c \
-                                    examples/tpm_io.c \
                                     examples/tpm_test_keys.c
 examples_bench_bench_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_bench_bench_DEPENDENCIES = src/libwolftpm.la
diff --git a/examples/csr/include.am b/examples/csr/include.am
index 649aac0..17e072d 100644
--- a/examples/csr/include.am
+++ b/examples/csr/include.am
@@ -5,8 +5,7 @@ if BUILD_EXAMPLES
 noinst_PROGRAMS += examples/csr/csr
 noinst_HEADERS  += examples/csr/csr.h
 examples_csr_csr_SOURCES      = examples/csr/csr.c \
-                                examples/tpm_test_keys.c \
-                                examples/tpm_io.c
+                                examples/tpm_test_keys.c
 examples_csr_csr_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_csr_csr_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/gpio/include.am b/examples/gpio/include.am
index 06fdd6e..a716dd1 100644
--- a/examples/gpio/include.am
+++ b/examples/gpio/include.am
@@ -8,18 +8,15 @@ noinst_PROGRAMS += examples/gpio/gpio_config \
 
 noinst_HEADERS  += examples/gpio/gpio.h
 
-examples_gpio_gpio_config_SOURCES      = examples/gpio/gpio_config.c \
-                                         examples/tpm_io.c
+examples_gpio_gpio_config_SOURCES      = examples/gpio/gpio_config.c
 examples_gpio_gpio_config_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_gpio_gpio_config_DEPENDENCIES = src/libwolftpm.la
 
-examples_gpio_gpio_read_SOURCES      = examples/gpio/gpio_read.c \
-                                       examples/tpm_io.c
+examples_gpio_gpio_read_SOURCES      = examples/gpio/gpio_read.c
 examples_gpio_gpio_read_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_gpio_gpio_read_DEPENDENCIES = src/libwolftpm.la
 
-examples_gpio_gpio_set_SOURCES      = examples/gpio/gpio_set.c \
-                                      examples/tpm_io.c
+examples_gpio_gpio_set_SOURCES      = examples/gpio/gpio_set.c
 examples_gpio_gpio_set_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_gpio_gpio_set_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/include.am b/examples/include.am
index a671e71..3781e0f 100644
--- a/examples/include.am
+++ b/examples/include.am
@@ -17,16 +17,6 @@ include examples/seal/include.am
 include examples/attestation/include.am
 
 dist_example_DATA+= examples/README.md \
-                    examples/tpm_io.c \
-                    examples/tpm_io_atmel.c \
-                    examples/tpm_io_barebox.c \
-                    examples/tpm_io_linux.c \
-                    examples/tpm_io_infineon.c \
-                    examples/tpm_io_microchip.c \
-                    examples/tpm_io_st.c \
-                    examples/tpm_io_qnx.c \
-                    examples/tpm_io_xilinx.c \
-                    examples/tpm_io.h \
                     examples/tpm_test_keys.c \
                     examples/tpm_test_keys.h \
                     examples/tpm_test.h
diff --git a/examples/keygen/include.am b/examples/keygen/include.am
index 7061f74..b3b40ae 100644
--- a/examples/keygen/include.am
+++ b/examples/keygen/include.am
@@ -6,29 +6,25 @@ noinst_HEADERS += examples/keygen/keygen.h
 
 noinst_PROGRAMS += examples/keygen/create_primary
 examples_keygen_create_primary_SOURCES      = examples/keygen/create_primary.c \
-                                              examples/tpm_test_keys.c \
-                                              examples/tpm_io.c
+                                              examples/tpm_test_keys.c
 examples_keygen_create_primary_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_keygen_create_primary_DEPENDENCIES = src/libwolftpm.la
 
 noinst_PROGRAMS += examples/keygen/keyload
 examples_keygen_keyload_SOURCES      = examples/keygen/keyload.c \
-                                       examples/tpm_test_keys.c \
-                                       examples/tpm_io.c
+                                       examples/tpm_test_keys.c
 examples_keygen_keyload_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_keygen_keyload_DEPENDENCIES = src/libwolftpm.la
 
 noinst_PROGRAMS += examples/keygen/keygen
 examples_keygen_keygen_SOURCES      = examples/keygen/keygen.c \
-                                      examples/tpm_test_keys.c \
-                                      examples/tpm_io.c
+                                      examples/tpm_test_keys.c
 examples_keygen_keygen_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_keygen_keygen_DEPENDENCIES = src/libwolftpm.la
 
 noinst_PROGRAMS += examples/keygen/keyimport
 examples_keygen_keyimport_SOURCES      = examples/keygen/keyimport.c \
-                                         examples/tpm_test_keys.c \
-                                         examples/tpm_io.c
+                                         examples/tpm_test_keys.c
 examples_keygen_keyimport_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_keygen_keyimport_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/management/include.am b/examples/management/include.am
index edf8fba..032337f 100644
--- a/examples/management/include.am
+++ b/examples/management/include.am
@@ -6,8 +6,7 @@ noinst_PROGRAMS += examples/management/flush
 
 noinst_HEADERS  += examples/management/flush.h
 
-examples_management_flush_SOURCES      = examples/management/flush.c \
-                                         examples/tpm_io.c
+examples_management_flush_SOURCES      = examples/management/flush.c
 examples_management_flush_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_management_flush_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/native/include.am b/examples/native/include.am
index 728083d..191bc87 100644
--- a/examples/native/include.am
+++ b/examples/native/include.am
@@ -4,8 +4,7 @@
 if BUILD_EXAMPLES
 noinst_PROGRAMS += examples/native/native_test
 noinst_HEADERS  += examples/native/native_test.h
-examples_native_native_test_SOURCES      = examples/native/native_test.c \
-                                           examples/tpm_io.c
+examples_native_native_test_SOURCES      = examples/native/native_test.c
 examples_native_native_test_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_native_native_test_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/nvram/include.am b/examples/nvram/include.am
index e0b47aa..1efaf04 100644
--- a/examples/nvram/include.am
+++ b/examples/nvram/include.am
@@ -6,22 +6,19 @@ noinst_HEADERS += examples/nvram/nvram.h
 
 noinst_PROGRAMS += examples/nvram/store
 examples_nvram_store_SOURCES      = examples/nvram/store.c \
-                                    examples/tpm_test_keys.c \
-                                    examples/tpm_io.c
+                                    examples/tpm_test_keys.c
 examples_nvram_store_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_nvram_store_DEPENDENCIES = src/libwolftpm.la
 
 noinst_PROGRAMS += examples/nvram/read
 examples_nvram_read_SOURCES      = examples/nvram/read.c \
-                                   examples/tpm_test_keys.c \
-                                   examples/tpm_io.c
+                                   examples/tpm_test_keys.c
 examples_nvram_read_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_nvram_read_DEPENDENCIES = src/libwolftpm.la
 
 noinst_PROGRAMS += examples/nvram/counter
 examples_nvram_counter_SOURCES      = examples/nvram/counter.c \
-                                   examples/tpm_test_keys.c \
-                                   examples/tpm_io.c
+                                   examples/tpm_test_keys.c
 examples_nvram_counter_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_nvram_counter_DEPENDENCIES = src/libwolftpm.la
 
diff --git a/examples/pcr/include.am b/examples/pcr/include.am
index e847ff0..1905d55 100644
--- a/examples/pcr/include.am
+++ b/examples/pcr/include.am
@@ -11,23 +11,19 @@ noinst_HEADERS  += examples/pcr/quote.h \
                    examples/pcr/pcr.h
 
 examples_pcr_quote_SOURCES      = examples/pcr/quote.c \
-                                  examples/tpm_test_keys.c \
-                                  examples/tpm_io.c
+                                  examples/tpm_test_keys.c
 examples_pcr_quote_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_pcr_quote_DEPENDENCIES = src/libwolftpm.la
 
-examples_pcr_read_pcr_SOURCES      = examples/pcr/read_pcr.c \
-                                     examples/tpm_io.c
+examples_pcr_read_pcr_SOURCES      = examples/pcr/read_pcr.c
 examples_pcr_read_pcr_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_pcr_read_pcr_DEPENDENCIES = src/libwolftpm.la
 
-examples_pcr_extend_SOURCES      = examples/pcr/extend.c \
-                                   examples/tpm_io.c
+examples_pcr_extend_SOURCES      = examples/pcr/extend.c
 examples_pcr_extend_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_pcr_extend_DEPENDENCIES = src/libwolftpm.la
 
-examples_pcr_reset_SOURCES      = examples/pcr/reset.c \
-                                  examples/tpm_io.c
+examples_pcr_reset_SOURCES      = examples/pcr/reset.c
 examples_pcr_reset_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_pcr_reset_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/pkcs7/include.am b/examples/pkcs7/include.am
index 5ee3e9e..117dcd7 100644
--- a/examples/pkcs7/include.am
+++ b/examples/pkcs7/include.am
@@ -5,8 +5,7 @@ if BUILD_EXAMPLES
 noinst_PROGRAMS += examples/pkcs7/pkcs7
 noinst_HEADERS  += examples/pkcs7/pkcs7.h
 examples_pkcs7_pkcs7_SOURCES      = examples/pkcs7/pkcs7.c \
-                                    examples/tpm_test_keys.c \
-                                    examples/tpm_io.c
+                                    examples/tpm_test_keys.c
 examples_pkcs7_pkcs7_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_pkcs7_pkcs7_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/seal/include.am b/examples/seal/include.am
index 8bef275..6a98838 100644
--- a/examples/seal/include.am
+++ b/examples/seal/include.am
@@ -8,14 +8,12 @@ noinst_PROGRAMS += examples/seal/seal \
 noinst_HEADERS  += examples/seal/seal.h
 
 examples_seal_seal_SOURCES      = examples/seal/seal.c \
-                                  examples/tpm_test_keys.c \
-                                  examples/tpm_io.c
+                                  examples/tpm_test_keys.c
 examples_seal_seal_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_seal_seal_DEPENDENCIES = src/libwolftpm.la
 
 examples_seal_unseal_SOURCES      = examples/seal/unseal.c \
-                                    examples/tpm_test_keys.c \
-                                    examples/tpm_io.c
+                                    examples/tpm_test_keys.c
 examples_seal_unseal_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_seal_unseal_DEPENDENCIES = src/libwolftpm.la
 
diff --git a/examples/timestamp/include.am b/examples/timestamp/include.am
index c314ca6..3d030c5 100644
--- a/examples/timestamp/include.am
+++ b/examples/timestamp/include.am
@@ -5,16 +5,14 @@ if BUILD_EXAMPLES
 noinst_PROGRAMS += examples/timestamp/signed_timestamp
 noinst_HEADERS  += examples/timestamp/signed_timestamp.h
 examples_timestamp_signed_timestamp_SOURCES      = examples/timestamp/signed_timestamp.c \
-                                                   examples/tpm_test_keys.c \
-                                                   examples/tpm_io.c
+                                                   examples/tpm_test_keys.c
 examples_timestamp_signed_timestamp_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_timestamp_signed_timestamp_DEPENDENCIES = src/libwolftpm.la
 
 
 noinst_PROGRAMS += examples/timestamp/clock_set
 noinst_HEADERS  += examples/timestamp/clock_set.h
-examples_timestamp_clock_set_SOURCES      = examples/timestamp/clock_set.c \
-                                            examples/tpm_io.c
+examples_timestamp_clock_set_SOURCES      = examples/timestamp/clock_set.c
 examples_timestamp_clock_set_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_timestamp_clock_set_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/examples/tls/include.am b/examples/tls/include.am
index 7d74cff..2d3fbc1 100644
--- a/examples/tls/include.am
+++ b/examples/tls/include.am
@@ -6,8 +6,7 @@ noinst_PROGRAMS += examples/tls/tls_client
 noinst_HEADERS  += examples/tls/tls_client.h \
                    examples/tls/tls_common.h
 examples_tls_tls_client_SOURCES      = examples/tls/tls_client.c \
-                                       examples/tpm_test_keys.c \
-                                       examples/tpm_io.c
+                                       examples/tpm_test_keys.c
 examples_tls_tls_client_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_tls_tls_client_DEPENDENCIES = src/libwolftpm.la
 
@@ -15,8 +14,7 @@ noinst_PROGRAMS += examples/tls/tls_client_notpm
 noinst_HEADERS  += examples/tls/tls_client.h \
                    examples/tls/tls_common.h
 examples_tls_tls_client_notpm_SOURCES      = examples/tls/tls_client_notpm.c \
-                                             examples/tpm_test_keys.c \
-                                             examples/tpm_io.c
+                                             examples/tpm_test_keys.c
 examples_tls_tls_client_notpm_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_tls_tls_client_notpm_DEPENDENCIES = src/libwolftpm.la
 
@@ -24,8 +22,7 @@ noinst_PROGRAMS += examples/tls/tls_server
 noinst_HEADERS  += examples/tls/tls_server.h \
                    examples/tls/tls_common.h
 examples_tls_tls_server_SOURCES      = examples/tls/tls_server.c \
-                                       examples/tpm_test_keys.c \
-                                       examples/tpm_io.c
+                                       examples/tpm_test_keys.c
 examples_tls_tls_server_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_tls_tls_server_DEPENDENCIES = src/libwolftpm.la
 
diff --git a/examples/wrap/include.am b/examples/wrap/include.am
index 6953c74..5aec5c5 100644
--- a/examples/wrap/include.am
+++ b/examples/wrap/include.am
@@ -4,8 +4,7 @@
 if BUILD_EXAMPLES
 noinst_PROGRAMS += examples/wrap/wrap_test
 noinst_HEADERS  += examples/wrap/wrap_test.h
-examples_wrap_wrap_test_SOURCES      = examples/wrap/wrap_test.c \
-                                       examples/tpm_io.c
+examples_wrap_wrap_test_SOURCES      = examples/wrap/wrap_test.c
 examples_wrap_wrap_test_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 examples_wrap_wrap_test_DEPENDENCIES = src/libwolftpm.la
 endif
diff --git a/hal/README.md b/hal/README.md
new file mode 100644
index 0000000..fa84435
--- /dev/null
+++ b/hal/README.md
@@ -0,0 +1,61 @@
+# 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` |
+| 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:
+
+```c
+#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:
+
+```c
+#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).
diff --git a/hal/include.am b/hal/include.am
new file mode 100644
index 0000000..c02041b
--- /dev/null
+++ b/hal/include.am
@@ -0,0 +1,18 @@
+# vim:ft=automake
+# All paths should be given relative to the root
+
+if BUILD_HAL
+src_libwolftpm_la_SOURCES += \
+                    hal/tpm_io.c \
+                    hal/tpm_io_atmel.c \
+                    hal/tpm_io_barebox.c \
+                    hal/tpm_io_linux.c \
+                    hal/tpm_io_infineon.c \
+                    hal/tpm_io_microchip.c \
+                    hal/tpm_io_st.c \
+                    hal/tpm_io_qnx.c \
+                    hal/tpm_io_xilinx.c
+endif
+
+nobase_include_HEADERS += hal/tpm_io.h
+EXTRA_DIST += hal/README.md
diff --git a/examples/tpm_io.c b/hal/tpm_io.c
similarity index 100%
rename from examples/tpm_io.c
rename to hal/tpm_io.c
diff --git a/examples/tpm_io.h b/hal/tpm_io.h
similarity index 71%
rename from examples/tpm_io.h
rename to hal/tpm_io.h
index 622f15b..c1b76a8 100644
--- a/examples/tpm_io.h
+++ b/hal/tpm_io.h
@@ -54,56 +54,68 @@
  *
  */
 
-#if defined(WOLFTPM_LINUX_DEV) || defined(WOLFTPM_SWTPM) || defined(WOLFTPM_WINAPI)
+#if defined(WOLFTPM_LINUX_DEV) || defined(WOLFTPM_SWTPM) || \
+    defined(WOLFTPM_WINAPI)
+
+/* HAL not required, so use NULL */
 #define TPM2_IoCb NULL
+
 #else
 
+#ifdef WOLFTPM_EXAMPLE_HAL
+
 #ifdef WOLFTPM_ADV_IO
-int TPM2_IoCb(TPM2_CTX*, int isRead, word32 addr, byte* buf, word16 size,
+WOLFTPM_API 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,
+WOLFTPM_API int TPM2_IoCb(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
     word16 xferSz, void* userCtx);
 #endif
-#endif /* !(WOLFTPM_LINUX_DEV || WOLFTPM_SWTPM || WOLFTPM_WINAPI) */
 
 /* Platform support, in alphabetical order */
 #ifdef WOLFTPM_I2C
+
 #if defined(__linux__)
-int TPM2_IoCb_Linux_I2C(TPM2_CTX* ctx, int isRead, word32 addr, byte* buf,
+WOLFTPM_LOCAL int TPM2_IoCb_Linux_I2C(TPM2_CTX* ctx, int isRead, word32 addr, byte* buf,
     word16 size, void* userCtx);
 #elif defined(WOLFSSL_STM32_CUBEMX)
-int TPM2_IoCb_STCubeMX_I2C(TPM2_CTX* ctx, int isRead, word32 addr,
+WOLFTPM_LOCAL int TPM2_IoCb_STCubeMX_I2C(TPM2_CTX* ctx, int isRead, word32 addr,
     byte* buf, word16 size, void* userCtx);
 #endif /* __linux__ */
+
 #else /* SPI */
+
 #if defined(WOLFSSL_ATMEL)
-int TPM2_IoCb_Atmel_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_Atmel_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
     word16 xferSz, void* userCtx);
 #elif defined(__BAREBOX__)
-int TPM2_IoCb_Barebox_SPI(TPM2_CTX* ctx, const byte* txBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_Barebox_SPI(TPM2_CTX* ctx, const byte* txBuf,
     byte* rxBuf, word16 xferSz, void* userCtx);
 #elif defined(__linux__)
-int TPM2_IoCb_Linux_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_Linux_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
     word16 xferSz, void* userCtx);
 #elif defined(WOLFSSL_STM32_CUBEMX)
-int TPM2_IoCb_STCubeMX_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_STCubeMX_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
     word16 xferSz, void* userCtx);
 #elif defined(__QNX__) || defined(__QNXTO__)
-int TPM2_IoCb_QNX_SPI(TPM2_CTX* ctx, const byte* txBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_QNX_SPI(TPM2_CTX* ctx, const byte* txBuf,
     byte* rxBuf, word16 xferSz, void* userCtx);
 #elif defined(__XILINX__)
-int TPM2_IoCb_Xilinx_SPI(TPM2_CTX* ctx, const byte* txBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_Xilinx_SPI(TPM2_CTX* ctx, const byte* txBuf,
     byte* rxBuf, word16 xferSz, void* userCtx);
 #elif defined(WOLFTPM_INFINEON_TRICORE)
-int TPM2_IoCb_Infineon_TriCore_SPI(TPM2_CTX* ctx, const byte* txBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_Infineon_TriCore_SPI(TPM2_CTX* ctx, const byte* txBuf,
     byte* rxBuf, word16 xferSz, void* userCtx);
 #elif defined(WOLFTPM_MICROCHIP)
-int TPM2_IoCb_Microchip_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
+WOLFTPM_LOCAL int TPM2_IoCb_Microchip_SPI(TPM2_CTX* ctx, const byte* txBuf, byte* rxBuf,
     word16 xferSz, void* userCtx);
-#endif /* WOLFSSL_ATMEL */
+#endif
+
 #endif /* WOLFTPM_I2C */
 
+#endif /* WOLFTPM_EXAMPLE_HAL */
+#endif /* !(WOLFTPM_LINUX_DEV || WOLFTPM_SWTPM || WOLFTPM_WINAPI) */
+
 #ifdef __cplusplus
     }  /* extern "C" */
 #endif
diff --git a/examples/tpm_io_atmel.c b/hal/tpm_io_atmel.c
similarity index 100%
rename from examples/tpm_io_atmel.c
rename to hal/tpm_io_atmel.c
diff --git a/examples/tpm_io_barebox.c b/hal/tpm_io_barebox.c
similarity index 100%
rename from examples/tpm_io_barebox.c
rename to hal/tpm_io_barebox.c
diff --git a/examples/tpm_io_infineon.c b/hal/tpm_io_infineon.c
similarity index 100%
rename from examples/tpm_io_infineon.c
rename to hal/tpm_io_infineon.c
diff --git a/examples/tpm_io_linux.c b/hal/tpm_io_linux.c
similarity index 100%
rename from examples/tpm_io_linux.c
rename to hal/tpm_io_linux.c
diff --git a/examples/tpm_io_microchip.c b/hal/tpm_io_microchip.c
similarity index 100%
rename from examples/tpm_io_microchip.c
rename to hal/tpm_io_microchip.c
diff --git a/examples/tpm_io_qnx.c b/hal/tpm_io_qnx.c
similarity index 100%
rename from examples/tpm_io_qnx.c
rename to hal/tpm_io_qnx.c
diff --git a/examples/tpm_io_st.c b/hal/tpm_io_st.c
similarity index 100%
rename from examples/tpm_io_st.c
rename to hal/tpm_io_st.c
diff --git a/examples/tpm_io_xilinx.c b/hal/tpm_io_xilinx.c
similarity index 100%
rename from examples/tpm_io_xilinx.c
rename to hal/tpm_io_xilinx.c
diff --git a/src/tpm2_linux.c b/src/tpm2_linux.c
index ea943d1..c1b2032 100644
--- a/src/tpm2_linux.c
+++ b/src/tpm2_linux.c
@@ -19,6 +19,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
  */
 
+#include <wolftpm/tpm2_types.h>
 
 #ifdef WOLFTPM_LINUX_DEV
 #include <wolftpm/tpm2_linux.h>
diff --git a/src/tpm2_swtpm.c b/src/tpm2_swtpm.c
index ea416a9..453c52d 100644
--- a/src/tpm2_swtpm.c
+++ b/src/tpm2_swtpm.c
@@ -32,6 +32,8 @@
  * See docs/SWTPM.md
  */
 
+#include <wolftpm/tpm2_types.h>
+
 #ifdef WOLFTPM_SWTPM
 #include <wolftpm/tpm2.h>
 #include <wolftpm/tpm2_swtpm.h>
diff --git a/src/tpm2_winapi.c b/src/tpm2_winapi.c
index 3fc2fd9..fcd8a46 100644
--- a/src/tpm2_winapi.c
+++ b/src/tpm2_winapi.c
@@ -20,6 +20,8 @@
  */
 
 
+#include <wolftpm/tpm2_types.h>
+
 #ifdef WOLFTPM_WINAPI
 #include <wolftpm/tpm2_winapi.h>
 
diff --git a/tests/include.am b/tests/include.am
index 33884fb..1aac9bc 100644
--- a/tests/include.am
+++ b/tests/include.am
@@ -5,9 +5,7 @@
 if BUILD_EXAMPLES
 check_PROGRAMS += tests/unit.test
 noinst_PROGRAMS += tests/unit.test
-tests_unit_test_SOURCES = \
-                  tests/unit_tests.c \
-                  examples/tpm_io.c
+tests_unit_test_SOURCES      = tests/unit_tests.c
 tests_unit_test_CFLAGS       = $(AM_CFLAGS)
 tests_unit_test_LDADD        = src/libwolftpm.la $(LIB_STATIC_ADD)
 tests_unit_test_DEPENDENCIES = src/libwolftpm.la