Using the ITM Viewer

The ITM Viewer window displays an ASCII or HEX representation of the data sequentially transmitted over ITM Port 0 in the ITM Viewer tab within µVision.

It may be used to view 8-bit, serial data generated from the target device, such as the output of a printf statement. This can be very useful during target debugging.

To use the ITM Viewer for Trace debug output:

1. Add ITM Stimulus Port register definitions to your source code.

   #define ITM_Port8(n)    (*((volatile unsigned char *)(0xE0000000+4*n)))
   #define ITM_Port16(n)   (*((volatile unsigned short*)(0xE0000000+4*n)))
   #define ITM_Port32(n)   (*((volatile unsigned long *)(0xE0000000+4*n)))
   
   #define DEMCR           (*((volatile unsigned long *)(0xE000EDFC)))
   #define TRCENA          0x01000000
   

2. Add a fputc function which writes to the ITM Stimulus Port 0 register to your source code. Adding this fputc function allows you to use printf for debug output. The ITM Viewer only works with ITM Port 0.

   struct __FILE { int handle; /* Add whatever you need here */ };
   FILE __stdout;
   FILE __stdin;
   
   int fputc(int ch, FILE *f) {
     if (DEMCR & TRCENA) {
       while (ITM_Port32(0) == 0);
       ITM_Port8(0) = ch;
     }
     return(ch);
   }
   

3. Add your Debug Trace Messages to your source code using printf.

   printf("AD value = 0x%04X\r\n", AD_value);
   

4. Set ITM Stimulus Port Port 0 bit to allow Trace to capture the ITM Port 0 information. Clear the Port 7..0 privilege bit to allow access to the Port 0 bit from User mode.
   
   
5. Select View - Serial Window - ITM Viewer to display the ITM Viewer window.
   
   

Note

• Only data transmitted over ITM Stimulus port 0 is displayed in the ITM window. Other ITM Ports can be monitored in the Trace Records Window where also ITM Port 0 is shown.