/* 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><aname="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.
