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| <h1>CMSIS Debug Support</h1> | |
| <hr> | |
| <h2>Cortex-M3 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> | |
| <h2>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 globel variable is used. A simple mechansim detects if a character is received. | |
| The project to test need to be build with debug information. | |
| </p> | |
| <p> | |
| The globale 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 enshure a proper handshake. | |
| </p> | |
| <pre> | |
| extern volatile int ITM_RxBuffer; /* variable to receive characters */ | |
| </pre> | |
| <p> | |
| A dedicated bit pattern is used to determin 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 int ITM_ReceiveChar (void) { | |
| int 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 int ITM_CheckChar (void) { | |
| if (ITM_RxBuffer == ITM_RXBUFFER_EMPTY) { | |
| return (0); /* no character available */ | |
| } else { | |
| return (1); /* character available */ | |
| } | |
| }</pre> | |
| <h2>ITM Debug Support in uVision</h2> | |
| <p> | |
| uVision uses in a debug session the <strong>Debug (printf) Viewer</strong> window to | |
| display the debug data. | |
| </p> | |
| <p>Direction microcontroller system -> uVision:</p> | |
| <ul> | |
| <li> | |
| Characters received via ITM communication channel 0 are written in a printf style | |
| to <strong>Debug (printf) Viewer</strong> window. | |
| </li> | |
| </ul> | |
| <p>Direction uVision -> microcontroller system:</p> | |
| <ul> | |
| <li>Check if <strong>ITM_RxBuffer</strong> variable is available (only performed once).</li> | |
| <li>Read character from <strong>Debug (printf) Viewer</strong> window.</li> | |
| <li>If <strong>ITM_RxBuffer</strong> empty write character to <strong>ITM_RxBuffer</strong>.</li> | |
| </ul> | |
| <p class="Note">Note</p> | |
| <ul> | |
| <li><p>Current solution does not use a buffer machanism for trasmitting the characters.</p> | |
| </li> | |
| </ul> | |
| <h2>RTX Kernel awareness in uVision</h2> | |
| <p> | |
| uVision / RTX are using a simple and efficient solution for RTX Kernel awareness. | |
| No format overhead is necessary.<br> | |
| uVsion debugger decodes the RTX events via the 32 / 16 / 8 bit ITM write access | |
| to ITM communication channel 31. | |
| </p> | |
| <p>Following RTX events are traced:</p> | |
| <ul> | |
| <li>Task Create / Delete event | |
| <ol> | |
| <li>32 bit access. Task start address is transmitted</li> | |
| <li>16 bit access. Task ID and Create/Delete flag are transmitted<br> | |
| High byte holds Create/Delete flag, Low byte holds TASK ID. | |
| </li> | |
| </ol> | |
| </li> | |
| <li>Task switch event | |
| <ol> | |
| <li>8 bit access. Task ID of current task is transmitted</li> | |
| </ol> | |
| </li> | |
| </ul> | |
| <p class="Note">Note</p> | |
| <ul> | |
| <li><p>Other RTOS information could be retrieved via memory read access in a polling mode manner.</p> | |
| </li> | |
| </ul> | |
| <p class="MsoNormal"><span lang="EN-GB"> </span></p> | |
| <hr> | |
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