I/O Ports

µVision defines a VTREG for each I/O port: i.e. PORTA. Do not mix-up VTREGs with Peripheral Registers for each port (for example, PIOA_OSR). Peripheral Registers can be accessed inside the CPU memory space. VTREGs are signals present on the pins.

It is easy to simulate input from external hardware. If you have a pulse train coming into a port pin, you can use a Signal Function to simulate the signal. For example, the following Signal Function inputs a square wave on PORTA pin 0 with a frequency of 1000Hz.

signal void one_thou_hz (void) {
  while (1) {                      /* repeat forever       */
    PORTA |= 1;                    /* set PORTA bit 0      */
    swatch (0.0005);               /* delay for .0005 secs */
    PORTA &= ~1;                   /* clear PORTA bit 0    */
    swatch (0.0005);               /* delay for .0005 secs */
  }                                /* repeat               */
}

The following command starts this Signal Function:

one_thou_hz ()

Refer to µVision Debug Functions for more information about User- and Signal Functions.

Simulating hardware that responds to output from a port pin is slightly more difficult. Two steps are required. First, write a µVision User- or Signal Function to perform the desired operations. Second, create a breakpoint that invokes the user function.

Suppose you use an output pin (PORTA bit 0) to enable or disable a LED. The following Signal Function uses the PORT2 VTREG to check the output from the CPU and to display a message in the Command window.

signal void check_pA0 (void) {
  if (PORTA & 1)) {                            /* Test PORTA bit 0 */
    printf ("LED is ON\n"); }                  /* 1? LED is ON */
  else { /* 0? LED is OFF */
    printf ("LED is OFF\n"):
  }
}

Now, add a breakpoint. The following command line adds a breakpoint for all writes to PORT2.

BS WRITE PORT2, 1, "check_p20 ()"

Whenever your target program writes to PORT2, the check_P20 function prints the current status of the LED. Refer to Breakpoints for more information about setting breakpoints.