Diff: NationZ_TPM20.cpp

Revision:

0:7cd000305b05

Child:

1:be4b399d5099

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/NationZ_TPM20.cpp	Thu Mar 19 17:46:21 2015 +0000
@@ -0,0 +1,700 @@
+/* mbed NationZ I2C TPM 2.0 Library,
+ * Copyright (c) 2015, Microsoft Coprporation Inc.
+ * by Stefan Thom (LordOfDorks) StefanTh@Microsoft.com, Stefan@ThomsR.Us
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+ 
+ #include "NationZ_TPM20.h"
+ 
+// Constructor for the I2C variant of the chip
+NTZTPM20::NTZTPM20(
+    PinName sda,
+    PinName scl
+    )
+{
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZI2C.Init: ");
+#endif
+    m_SPITpmDev = NULL;
+    m_SPICSTpmDev = NULL;
+    m_I2CTpmDev = new I2C(sda, scl);
+    m_I2CTpmDev->frequency(400000);
+    m_ExclusiveAccess = false;
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK.\n\r");
+#endif
+}
+
+// Constructor for the SPI variant of the chip
+NTZTPM20::NTZTPM20(
+    PinName mosi,
+    PinName miso,
+    PinName clk,
+    PinName cs
+    )
+{
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZSPI.Init: ");
+#endif
+    m_I2CTpmDev = NULL;
+    m_SPITpmDev = new SPI(mosi, miso, clk);
+    m_SPITpmDev->format(8, 0);
+    m_SPITpmDev->frequency(5000000);
+    m_SPICSTpmDev = new DigitalOut(cs);
+    *m_SPICSTpmDev = 1;
+    m_ExclusiveAccess = false;
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK.\n\r");
+#endif
+}
+
+// Release all held resources
+NTZTPM20::~NTZTPM20()
+{
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.Destroy: ");
+#endif
+    if(m_I2CTpmDev != NULL)
+    {
+        delete m_I2CTpmDev;
+        m_I2CTpmDev = NULL;
+    }
+    if(m_SPITpmDev != NULL)
+    {
+        delete m_SPITpmDev;
+        m_SPITpmDev = NULL;
+    }
+    if(m_SPICSTpmDev != NULL)
+    {
+        delete m_SPICSTpmDev;
+        m_SPICSTpmDev = NULL;
+    }
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK.\n\r");
+#endif
+}
+
+uint32_t
+NTZTPM20::Execute(
+    uint8_t* pbCmd,
+    uint32_t cbCmd,
+    uint8_t* pbRsp,
+    uint32_t cbRsp,
+    uint32_t timeout
+    )
+{
+    uint32_t result = 0;
+    Timeout watchdog;
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.ExecuteWaitForAccess.");
+#endif
+
+    // Only one caller should be talking to the TPM at any given time
+    while(m_ExclusiveAccess)
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf(".");
+#endif
+        wait_us(500);
+    }
+    m_ExclusiveAccess = true;
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK\n\r");
+#endif
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.SetupTimeout\n\r");
+#endif
+    // Setup TPM timeout
+    m_TimeoutTriggered = false;
+    watchdog.attach(this, &NTZTPM20::TimeoutTrigger, 0.0001 * timeout);
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.Execute: ");
+    for(uint32_t n = 0; n < cbCmd; n++) printf("%02x ", pbCmd[n]);
+    printf("\n\r");
+#endif
+    
+    // Execute command on the TPM
+    if(m_I2CTpmDev != NULL)
+    {
+        result = ExecuteI2C(pbCmd, cbCmd, pbRsp, cbRsp);
+    }
+    else if(m_SPITpmDev != NULL)
+    {
+        result = ExecuteSPI(pbCmd, cbCmd, pbRsp, cbRsp);
+    }
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.Response: ");
+    for(uint32_t n = 0; n < result; n++) printf("%02x ", pbRsp[n]);
+    printf("\n\r");
+#endif
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.CancelTimeout\n\r");
+#endif
+    // Cleanup
+    watchdog.detach();
+    m_ExclusiveAccess = false;
+    return result;
+}
+
+uint32_t
+NTZTPM20::ParseResponseHeader(
+    uint8_t* pbRsp,
+    uint32_t rspLen,
+    uint16_t* rspTag,
+    uint32_t* rspSize,
+    uint32_t* cursor
+    )
+{
+    uint32_t rspResponseCode = 0;
+
+    // Check that the response header is well formatted
+    if(rspLen < (sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint32_t)))
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf("NTZ.ResponseHdr.rspLen = 0x%08x\n\r", rspLen);
+#endif
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+    
+    // Read the header components
+    *rspTag = BYTEARRAY_TO_UINT16(pbRsp, *cursor);
+    *cursor += sizeof(uint16_t);
+    *rspSize = BYTEARRAY_TO_UINT32(pbRsp, *cursor);
+    *cursor += sizeof(uint32_t);
+    rspResponseCode = BYTEARRAY_TO_UINT32(pbRsp, *cursor);
+    *cursor += sizeof(uint32_t);
+
+    // Check the components
+    if(((*rspTag != TPM_ST_NO_SESSIONS) && (*rspTag != TPM_ST_SESSIONS)) ||
+       (*rspSize != rspLen))
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf("NTZ.ResponseHdr.rspTag = 0x%04x.rspLen=0x%08x\n\r", *rspTag, rspLen);
+#endif
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+
+Cleanup:    
+    return rspResponseCode;
+}
+
+uint32_t
+NTZTPM20::TPM2_Startup(
+    uint16_t startupType
+    )
+{
+    uint32_t rspLen = 0;
+    uint16_t rspTag = 0;
+    uint32_t rspSize = 0;
+    uint32_t rspResponseCode = 0;
+    uint32_t cursor = 0;
+    uint8_t tpmCmd[] = {0x80, 0x01, 0x00, 0x00, 0x00, 0x0c, 0x00, 0x00, 0x01, 0x44, 0x00, 0x00};
+    UINT16_TO_BYTEARRAY(startupType, tpmCmd, sizeof(tpmCmd) - 2);
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_Startup(0x%04x)\n\r", startupType);
+#endif
+
+    if((rspLen = Execute(tpmCmd, sizeof(tpmCmd), tpmCmd, sizeof(tpmCmd), 10000)) == 0)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+    if((rspResponseCode = ParseResponseHeader(tpmCmd, rspLen, &rspTag, &rspSize, &cursor)) != TPM_RC_SUCCESS)
+    {
+        goto Cleanup;
+    }
+    
+    if(rspSize != 0x0000000a)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+    }
+
+Cleanup:    
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_Startup.ResponseCode = 0x%08x\n\r", rspResponseCode);
+#endif
+    return rspResponseCode;
+}
+
+uint32_t
+NTZTPM20::TPM2_Shutdown(
+    uint16_t shutdownType
+    )
+{
+    uint32_t rspLen = 0;
+    uint16_t rspTag = 0;
+    uint32_t rspSize = 0;
+    uint32_t rspResponseCode = 0;
+    uint32_t cursor = 0;
+    uint8_t tpmCmd[] = {0x80, 0x01, 0x00, 0x00, 0x00, 0x0c, 0x00, 0x00, 0x01, 0x45, 0x00, 0x00};
+    UINT16_TO_BYTEARRAY(shutdownType, tpmCmd, sizeof(tpmCmd) - 2);
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_Shutdown(0x%04x)\n\r", shutdownType);
+#endif
+
+    if((rspLen = Execute(tpmCmd, sizeof(tpmCmd), tpmCmd, sizeof(tpmCmd), 120000)) == 0)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+    if((rspResponseCode = ParseResponseHeader(tpmCmd, rspLen, &rspTag, &rspSize, &cursor)) != TPM_RC_SUCCESS)
+    {
+        goto Cleanup;
+    }
+
+    if(rspSize != 0x0000000a)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+    }
+
+Cleanup:
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_Shutdown.ResponseCode = 0x%08x\n\r", rspResponseCode);
+#endif
+    return rspResponseCode;
+}
+
+uint32_t
+NTZTPM20::TPM2_SelfTest(
+    uint8_t fullTest
+    )
+{
+    uint32_t rspLen = 0;
+    uint16_t rspTag = 0;
+    uint32_t rspSize = 0;
+    uint32_t rspResponseCode = 0;
+    uint32_t cursor = 0;
+    uint8_t tpmCmd[] = {0x80, 0x01, 0x00, 0x00, 0x00, 0x0b, 0x00, 0x00, 0x01, 0x43, 0x00};
+    tpmCmd[sizeof(tpmCmd) - 1] = fullTest;
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_SelfTest(0x%02x)\n\r", fullTest);
+#endif
+
+    if((rspLen = Execute(tpmCmd, sizeof(tpmCmd), tpmCmd, sizeof(tpmCmd), 5000)) == 0)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+    if((rspResponseCode = ParseResponseHeader(tpmCmd, rspLen, &rspTag, &rspSize, &cursor)) != TPM_RC_SUCCESS)
+    {
+        goto Cleanup;
+    }
+
+    if(rspSize != 0x0000000a)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+    }
+
+Cleanup:
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_SelfTest.ResponseCode = 0x%08x\n\r", rspResponseCode);
+#endif
+    return rspResponseCode;
+}
+
+uint32_t
+NTZTPM20::TPM2_GetRandom(
+    uint16_t bytesRequested,
+    uint8_t* randomBytes
+    )
+{
+    uint32_t cursor = 0;
+    uint32_t rspLen = 0;
+    uint16_t rspTag = 0;
+    uint32_t rspSize = 0;
+    uint32_t rspResponseCode = 0;
+    uint32_t tpmMax = sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint32_t) + sizeof(uint16_t) + bytesRequested;
+    uint8_t* tpmCmd = new uint8_t[tpmMax];
+    uint16_t bytesReturned = 0;
+    
+    if(tpmCmd == NULL)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+
+    // Build command
+    UINT16_TO_BYTEARRAY(TPM_ST_NO_SESSIONS, tpmCmd, cursor);
+    cursor += sizeof(uint16_t) + sizeof(cursor);
+    UINT32_TO_BYTEARRAY(TPM_CC_GetRandom, tpmCmd, cursor);
+    cursor += sizeof(TPM_CC_GetRandom);
+    UINT16_TO_BYTEARRAY(bytesRequested, tpmCmd, cursor);
+    cursor += sizeof(bytesRequested);
+    UINT32_TO_BYTEARRAY(cursor, tpmCmd, sizeof(uint16_t));
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_GetRandom(%d)\n\r", bytesRequested);
+#endif
+
+    if((rspLen = Execute(tpmCmd, cursor, tpmCmd, tpmMax, 5000)) == 0)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+    cursor = 0;
+    if((rspResponseCode = ParseResponseHeader(tpmCmd, rspLen, &rspTag, &rspSize, &cursor)) != TPM_RC_SUCCESS)
+    {
+        goto Cleanup;
+    }
+
+    if(rspSize != tpmMax)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+
+    // Copy the random bytes out
+    bytesReturned = BYTEARRAY_TO_UINT16(tpmCmd, cursor);
+    cursor += sizeof(uint16_t);
+    memcpy(randomBytes, &tpmCmd[cursor], (size_t)min(bytesReturned, bytesRequested));
+ 
+ Cleanup:
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_GetRandom.ResponseCode = 0x%08x\n\r", rspResponseCode);
+#endif
+    if(tpmCmd != NULL)
+    {
+        delete[] tpmCmd;
+        tpmCmd = NULL;
+    }
+    return rspResponseCode;
+}
+
+uint32_t
+NTZTPM20::TPM2_StirRandom(
+    uint16_t inDataLen,
+    uint8_t* inData
+    )
+{
+    uint32_t cursor = 0;
+    uint32_t rspLen = 0;
+    uint16_t rspTag = 0;
+    uint32_t rspSize = 0;
+    uint32_t rspResponseCode = 0;
+    uint32_t tpmMax = sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint32_t) + sizeof(uint16_t) + inDataLen;
+    uint8_t* tpmCmd = new uint8_t[tpmMax];
+    
+    if(tpmCmd == NULL)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+
+    // Build command
+    UINT16_TO_BYTEARRAY(TPM_ST_NO_SESSIONS, tpmCmd, cursor);
+    cursor += sizeof(uint16_t) + sizeof(cursor);
+    UINT32_TO_BYTEARRAY(TPM_CC_StirRandom, tpmCmd, cursor);
+    cursor += sizeof(TPM_CC_GetRandom);
+    UINT16_TO_BYTEARRAY(inDataLen, tpmCmd, cursor);
+    cursor += sizeof(inDataLen);
+    memcpy(&tpmCmd[cursor], inData, inDataLen);
+    cursor += inDataLen;
+    UINT32_TO_BYTEARRAY(cursor, tpmCmd, sizeof(uint16_t));
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_StirRandom(%d)\n\r", inDataLen);
+#endif
+
+    if((rspLen = Execute(tpmCmd, cursor, tpmCmd, tpmMax, 5000)) == 0)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+    cursor = 0;
+    if((rspResponseCode = ParseResponseHeader(tpmCmd, rspLen, &rspTag, &rspSize, &cursor)) != TPM_RC_SUCCESS)
+    {
+        goto Cleanup;
+    }
+
+    if(rspSize != 0x0000000a)
+    {
+        rspResponseCode = TPM_RC_FAILURE;
+        goto Cleanup;
+    }
+
+ Cleanup:
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZ.TPM2_StirRandom.ResponseCode = 0x%08x\n\r", rspResponseCode);
+#endif
+    if(tpmCmd != NULL)
+    {
+        delete[] tpmCmd;
+        tpmCmd = NULL;
+    }
+    return rspResponseCode;
+}
+
+void
+NTZTPM20::TimeoutTrigger(
+    void
+    )
+{
+    m_TimeoutTriggered = true;
+}
+
+uint32_t
+NTZTPM20::ExecuteI2C(
+    uint8_t* pbCmd,
+    uint32_t cbCmd,
+    uint8_t* pbRsp,
+    uint32_t cbRsp
+    )
+{
+    uint32_t result = 0;
+    uint32_t waitPeriod = 0;
+    uint8_t retry = 0;
+    uint32_t index = 0;
+    uint32_t rspLen = 0;
+
+    // Send the command buffer. Since the TPM may be sleeping we have to retry until the command is accepted
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZI2C.DeviceWakeup.");
+#endif
+    while((m_I2CTpmDev->write(m_I2CDevice_Address, (const char *)pbCmd, cbCmd, false) != 0) && (!m_TimeoutTriggered))
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf(".");
+#endif
+        wait_us(100);
+    }
+    
+    // See if device wakeup timed out
+    if(m_TimeoutTriggered)
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf("Timeout\n\r");
+#endif
+        goto Cleanup;
+    }
+    
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK\n\rNTZI2C.SentBytes = %d\n\rNTZI2C.WaitForCompletion.", cbCmd);
+#endif
+
+    // Wait for the TPM to have a response and then read the TPM response header consisting of TAG, SIZE and RETURNCODE
+    waitPeriod = 100;
+    while((m_I2CTpmDev->read(m_I2CDevice_Address, (char *)&pbRsp[index], (sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint32_t)), false) != 0) && (!m_TimeoutTriggered))
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf(".");
+#endif
+        wait_us(waitPeriod);
+
+        // Progressively wait longer to give the TPM some time to think
+        if(retry++ > 10)
+        {
+            waitPeriod *= 10;
+            retry = 0;
+        }
+    }
+    
+    if(m_TimeoutTriggered)
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf("Timeout\n\r");
+#endif
+        goto Cleanup;
+    }
+
+    // Move the write pointer
+    index += (sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint32_t));
+    
+    // Get the response size from the buffer and see how much we can read
+    rspLen = min(BYTEARRAY_TO_UINT32(pbRsp, sizeof(uint16_t)), cbRsp);
+   
+    // Read the remaining data from the TPM
+    if((rspLen - index) > 0)
+    {
+        while((m_I2CTpmDev->read(m_I2CDevice_Address, (char *)&pbRsp[index], rspLen - index, false) != 0) && (!m_TimeoutTriggered))
+        {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+            printf(".");
+#endif
+            wait_us(100);
+        }
+        if(m_TimeoutTriggered)
+        {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+            printf("Timeout\n\r");
+#endif
+            goto Cleanup;
+        }
+    }
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK\n\rNTZI2C.ReadBytes = %d\r\n", rspLen);
+#endif
+
+    result = rspLen;
+
+Cleanup:
+    return result;
+}
+
+uint32_t
+NTZTPM20::ExecuteSPI(
+    uint8_t* pbCmd,
+    uint32_t cbCmd,
+    uint8_t* pbRsp,
+    uint32_t cbRsp
+    )
+{
+    uint32_t result = 0;
+    uint32_t waitPeriod = 0;
+    uint8_t retry = 0;
+    uint8_t statusByte = 0;
+    uint32_t index = 0;
+
+    // Lock the SPI bus for this operation
+    *m_SPICSTpmDev = 0;
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT    
+    printf("NTZSPI.Wakeup.");
+#endif
+
+    // Wake the TPM up
+    do
+    {
+        if((statusByte = m_SPITpmDev->write(0xAA)) != 0xAA)
+        {
+            wait_us(10);
+        }
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf(".");
+#endif
+    } while((statusByte != 0xAA) && (!m_TimeoutTriggered));
+
+    // If the operation timed out bail
+    if((statusByte != 0xAA) && (m_TimeoutTriggered))
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf("Timeout\r\n");
+#endif
+        goto Cleanup;
+    }
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK\r\nNTZSPI.CommandReady\r\n");
+#endif
+    // Signal commandReady to the TPM
+    m_SPITpmDev->write(0xA5);
+
+    // Send the command buffer
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZSPI.SendBytes = %d\r\n", cbCmd);
+#endif
+    for(uint32_t n = 0; n < cbCmd; n ++)
+    {
+        m_SPITpmDev->write(pbCmd[n]);
+    }
+
+    // Release the bus while the TPM is thinking
+    *m_SPICSTpmDev = 1;
+
+    // Wait for a response
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZSPI.WaitForCompletion.");
+#endif
+    waitPeriod = 100;
+    do
+    {
+        wait_us(waitPeriod);
+
+        // Progressively wait longer to give the TPM some time to think
+        if(retry++ > 10)
+        {
+            waitPeriod *= 10;
+            retry = 0;
+        }
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf(".");
+#endif
+
+        // Lock the bus for this operation
+        *m_SPICSTpmDev = 0;
+        
+        // Poke the TPM so see if it is ready
+        if((pbRsp[index] = m_SPITpmDev->write(0xAA)) != 0xAA)
+        {
+            index++;
+
+            // Read the TPM response header
+            for(; index < (sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint32_t)); index++)
+            {
+                pbRsp[index] = m_SPITpmDev->write(0xFF);
+            }
+            
+            uint32_t rspLen = BYTEARRAY_TO_UINT32(pbRsp, sizeof(uint16_t));
+            result = min(rspLen, cbRsp);
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+            if(result < rspLen)
+            {
+                printf("NTZSPI.ResponseBufferTooShortBy = %d", rspLen - result);
+            }
+#endif
+
+            // Read the remainder of the response if there is one
+            for(; index < result; index++)
+            {
+                pbRsp[index] = m_SPITpmDev->write(0xFF);
+            }
+        }
+       
+        // release the bus
+        *m_SPICSTpmDev = 1;
+    }
+    while((pbRsp[0] == 0xAA) && (!m_TimeoutTriggered));
+        
+    if((pbRsp[0] == 0xAA) && (m_TimeoutTriggered))
+    {
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+        printf("Timeout\r\n");
+#endif
+        goto Cleanup;
+    }
+
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("OK\n\rNTZSPI.ReadBytes = %d\n\r", index);
+#endif
+
+Cleanup:
+    // Make sure to release the bus
+    *m_SPICSTpmDev = 1;
+
+    // Send the TPM back to sleep
+#ifdef TPM_NTZ_DEBUG_OUTPUT
+    printf("NTZSPI.Sleep\r\n");
+#endif
+    *m_SPICSTpmDev = 0;
+    m_SPITpmDev->write(0x5A);
+    *m_SPICSTpmDev = 1;
+    return result;
+}