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