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HTML
240 lines
9.7 KiB
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<body>
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<h1>CMSIS Debug Support</h1>
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<p align="center">This file describes the CMSIS Debug support available with CMSIS (starting V1.30).</p>
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<p align="center">Version: 1.02 - 25. July 2011</p>
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<p class="TinyT">Information in this file, the accompany manuals, and software is<br>
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Copyright <20> ARM Ltd.<br>All rights reserved.
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</p>
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<hr>
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<p><span style="FONT-WEIGHT: bold">Revision History</span></p>
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<ul>
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<li>Version 1.00: Initial Release. </li>
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<li>Version 1.01: Internal Review. </li>
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<li>Version 1.02: Removed product specific information. </li>
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</ul>
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<hr>
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<h2>Contents</h2>
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<ol>
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<li class="LI2"><a href="#About">About</a></li>
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<li class="LI2"><a href="#ITM_DbgAcc">Cortex-M3 / Cortex-M4 ITM Debug Access</a></li>
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<li class="LI2"><a href="#DbgIn_DbgOut">Debug IN / OUT functions</a></li>
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<li class="LI2"><a href="#ITM_DbgSup">ITM Debug Support in Debugger</a></li>
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</ol>
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<p> </p>
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<h2><a name="About"></a>About</h2>
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<p>
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CMSIS provides for Cortex-M3 / Cortex-M4 processor based microcontrollers debug support via the Instrumented Trace Macrocell (ITM).
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This document describes the available CMSIS Debug functions and the used methods.
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</p>
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<p> </p>
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<h2><a name="ITM_DbgAcc"></a>Cortex-M3 / Cortex-M4 ITM Debug Access</h2>
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<p>
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The Cortex-M3 incorporates the Instrumented Trace Macrocell (ITM) that provides together with
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the Serial Viewer Output trace capabilities for the microcontroller system. The ITM has
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32 communication channels which are able to transmit 32 / 16 / 8 bit values; two ITM
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communication channels are used by CMSIS to output the following information:
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</p>
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<ul>
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<li>ITM Channel 0: used for printf-style output via the debug interface.</li>
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<li>ITM Channel 31: is reserved for RTOS kernel awareness debugging.</li>
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</ul>
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<p> </p>
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<h2><a name="DbgIn_DbgOut"></a>Debug IN / OUT functions</h2>
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<p>CMSIS provides following debug functions:</p>
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<ul>
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<li>ITM_SendChar (uses ITM channel 0)</li>
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<li>ITM_ReceiveChar (uses global variable)</li>
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<li>ITM_CheckChar (uses global variable)</li>
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</ul>
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<h3>ITM_SendChar</h3>
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<p>
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<strong>ITM_SendChar</strong> is used to transmit a character over ITM channel 0 from
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the microcontroller system to the debug system. <br>
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Only a 8 bit value is transmitted.
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</p>
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<pre>
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static __INLINE uint32_t ITM_SendChar (uint32_t ch)
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{
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/* check if debugger connected and ITM channel enabled for tracing */
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if ((CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA) &&
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(ITM->TCR & ITM_TCR_ITMENA) &&
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(ITM->TER & (1UL << 0)) )
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{
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while (ITM->PORT[0].u32 == 0);
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ITM->PORT[0].u8 = (uint8_t)ch;
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}
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return (ch);
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}</pre>
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<h3>ITM_ReceiveChar</h3>
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<p>
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ITM communication channel is only capable for OUT direction. For IN direction
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a global variable is used. A simple mechanism detects if a character is received.
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The project to test need to be build with debug information.
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</p>
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<p>
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The global variable <strong>ITM_RxBuffer</strong> is used to transmit a 8 bit value from debug system
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to microcontroller system. <strong>ITM_RxBuffer</strong> is 32 bit wide to
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ensure a proper handshake.
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</p>
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<pre>
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extern volatile int32_t ITM_RxBuffer; /* variable to receive characters */
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</pre>
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<p>
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A dedicated bit pattern is used to determine if <strong>ITM_RxBuffer</strong> is empty
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or contains a valid value.
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</p>
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<pre>
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#define ITM_RXBUFFER_EMPTY 0x5AA55AA5 /* value identifying ITM_RxBuffer is ready for next character */
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</pre>
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<p>
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<strong>ITM_ReceiveChar</strong> is used to receive a 8 bit value from the debug system. The function is nonblocking.
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It returns the received character or '-1' if no character was available.
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</p>
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<pre>
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static __INLINE int32_t ITM_ReceiveChar (void) {
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int32_t ch = -1; /* no character available */
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if (ITM_RxBuffer != ITM_RXBUFFER_EMPTY) {
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ch = ITM_RxBuffer;
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ITM_RxBuffer = ITM_RXBUFFER_EMPTY; /* ready for next character */
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}
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return (ch);
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}
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</pre>
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<h3>ITM_CheckChar</h3>
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<p>
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<strong>ITM_CheckChar</strong> is used to check if a character is received.
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</p>
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<pre>
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static __INLINE int32_t ITM_CheckChar (void) {
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if (ITM_RxBuffer == ITM_RXBUFFER_EMPTY) {
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return (0); /* no character available */
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} else {
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return (1); /* character available */
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}
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}</pre>
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<p> </p>
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<h2><a name="ITM_DbgSup"></a>ITM Debug Support in a Debugger</h2>
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<p>
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The Debugger shall offer a dedicated console window for printf style debug input and output using the CMSIS defined ITM methods described above.
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</p>
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<p>Direction: Microcontroller -> Debugger:</p>
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<ul>
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<li>
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at the beginning of a debug session the debugger shall enable ITM trace on channel 0 and continuously snoop for channel 0 data on the ITM trace
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stream it receives from the Microcontroller's CoreSight ITM unit
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</li>
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<li>
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data received via the ITM communication channel 0 is interpreted as charater and gets redirected into the dedicated <strong>Console Window</strong>
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</li>
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</ul>
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<p>Direction: Debugger -> Microcontroller:</p>
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<ul>
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<li>
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at the beginning of a debug session the debugger shall seek for the presence of the global variable named <strong>ITM_RxBuffer</strong> in the debug
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information of the application being loaded
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</li>
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<li>
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strings entered into the <strong>Console Window</strong> are written by the debugger as a stream of char values via the variable <strong>ITM_RxBuffer</strong>.
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</li>
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<li>
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the debugger writes the next character into the <strong>ITM_RxBuffer</strong> only once the value has been read and the <strong>ITM_RXBUFFER_EMPTY</strong> value being set.
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(refer to: ITM_ReceiveChar()).
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</ul>
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