Instrumented Trace Macrocell (ITM) HAL API

HAL API for initializing the ITM and setting SWO debug output.
Actual debug output implemented as SWO FileHandle.

drivers/SerialWireOutput.h

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+/* mbed Microcontroller Library
+ * Copyright (c) 2017 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if defined(DEVICE_ITM)
+
+#include "hal/itm_api.h"
+#include "platform/FileHandle.h"
+
+class SerialWireOutput : public FileHandle {
+public:
+    SerialWireOutput(void)
+    {
+        /* Initialize ITM using internal init function. */
+        mbed_itm_init();
+    }
+
+    virtual ssize_t write(const void *buffer, size_t size)
+    {
+        const unsigned char *buf = static_cast<const unsigned char *>(buffer);
+
+        /* Send buffer one character at a time over the ITM SWO port */
+        for (size_t i = 0; i < size; i++) {
+            mbed_itm_send(ITM_PORT_SWO, buf[i]);
+        }
+        return size;
+    }
+
+    virtual ssize_t read(void *buffer, size_t size)
+    {
+        /* Reading is not supported by this file handle */
+        return -EBADF;
+    }
+
+    virtual off_t seek(off_t offset, int whence = SEEK_SET)
+    {
+        /* Seeking is not support by this file handler */
+        return -ESPIPE;
+    }
+
+    virtual off_t size()
+    {
+        /* Size is not defined for this file handle */
+        return -EINVAL;
+    }
+
+    virtual int isatty()
+    {
+        /* File handle is used for terminal output */
+        return true;
+    }
+
+    virtual int close()
+    {
+        return 0;
+    }
+};
+
+#endif

hal/itm_api.h

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+/* mbed Microcontroller Library
+ * Copyright (c) 2017 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef MBED_ITM_API_H
+#define MBED_ITM_API_H
+
+#if defined(DEVICE_ITM)
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @defgroup hal_itm_port ITM Stimulus Ports
+ *
+ * @{
+ */
+
+enum {
+    ITM_PORT_SWO = 0
+};
+
+/**@}*/
+
+/**
+ * \defgroup itm_hal Instrumented Trace Macrocell HAL API
+ * @{
+ */
+
+/**
+ * @brief      Target specific initialization function.
+ *             This function is responsible for initializing and configuring 
+ *             the debug clock for the ITM and setting up the SWO pin for 
+ *             debug output.
+ *             
+ *             The only Cortex-M register that should be modified is the clock
+ *             prescaler in TPI->ACPR.
+ *             
+ *             The generic mbed_itm_init initialization function will setup: 
+ *             
+ *                  ITM->LAR
+ *                  ITM->TPR
+ *                  ITM->TCR
+ *                  ITM->TER
+ *                  TPI->SPPR
+ *                  TPI->FFCR
+ *                  DWT->CTRL
+ *                  
+ *             for SWO output on stimulus port 0.
+ */
+void itm_init(void);
+
+/**
+ * @brief      Initialization function for both generic registers and target specific clock and pin.
+ */
+void mbed_itm_init(void);
+
+/**
+ * @brief      Send data over ITM stimulus port.
+ *
+ * @param[in]  port  The stimulus port to send data over.
+ * @param[in]  data  The data to send.
+ *
+ * @return     value of data sent.
+ */
+uint32_t mbed_itm_send(uint32_t port, uint32_t data);
+
+/**@}*/
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+
+#endif /* MBED_ITM_API_H */

hal/mbed_itm_api.c

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+/* mbed Microcontroller Library
+ * Copyright (c) 2017 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if defined(DEVICE_ITM)
+
+#include "hal/itm_api.h"
+#include "cmsis.h"
+
+#include <stdbool.h>
+
+#define ITM_ENABLE_WRITE 0xC5ACCE55 
+
+#define SWO_NRZ 0x02
+#define SWO_STIMULUS_PORT 0x01
+
+void mbed_itm_init(void)
+{
+    static bool do_init = true;
+
+    if (do_init) {
+        do_init = false;
+
+        itm_init();
+
+        /* Enable write access to ITM registers. */
+        ITM->LAR  = ITM_ENABLE_WRITE;
+
+        /* Trace Port Interface Selected Pin Protocol Register. */
+        TPI->SPPR = (SWO_NRZ << TPI_SPPR_TXMODE_Pos);
+
+        /* Trace Port Interface Formatter and Flush Control Register */
+        TPI->FFCR = (1 << TPI_FFCR_TrigIn_Pos);
+
+        /* Data Watchpoint and Trace Control Register */
+        DWT->CTRL = (1 << DWT_CTRL_CYCTAP_Pos)       |
+                    (0xF << DWT_CTRL_POSTINIT_Pos)   |
+                    (0xF << DWT_CTRL_POSTPRESET_Pos) |
+                    (1 << DWT_CTRL_CYCCNTENA_Pos);
+
+        /* Trace Privilege Register.
+         * Disable access to trace channel configuration from non-privileged mode.
+         */
+        ITM->TPR  = 0x0;
+
+        /* Trace Control Register */
+        ITM->TCR  = (1 << ITM_TCR_TraceBusID_Pos) | 
+                    (1 << ITM_TCR_DWTENA_Pos)     | 
+                    (1 << ITM_TCR_SYNCENA_Pos)    |
+                    (1 << ITM_TCR_ITMENA_Pos);
+
+        /* Trace Enable Register */
+        ITM->TER = SWO_STIMULUS_PORT;    
+    }
+}
+
+uint32_t mbed_itm_send(uint32_t port, uint32_t data)
+{
+    /* Check if ITM and port is enabled */
+    if (((ITM->TCR & ITM_TCR_ITMENA_Msk) != 0UL) &&      /* ITM enabled */
+        ((ITM->TER & (1UL << port)     ) != 0UL)   )     /* ITM Port enabled */
+    {
+        /* write data to port */
+        ITM->PORT[port].u32 = data;
+
+        /* Wait until data has been clocked out */
+        while (ITM->PORT[port].u32 == 0UL) {
+            __NOP();
+        }
+    }
+
+    return data;
+}
+
+#endif // defined(DEVICE_ITM)