Page 455 - Programming Microcontrollers in C

440 Chapter 8 MCORE, A RISC Machine

This location is entry number 6 in the vector table. The main()
function is broken into two sections, the initialization, and the
applications section. In initialization, inituart() establishes
connection with the serial I/O functions. The function
attach_semaphore(‘a’) connects a semaphore to this process.
This semaphore is passed to the kpinit() function along with a
pointer to the beginning of the array a[] and also its length. The
address of the interrupt handler is placed into the autovector location
by the vector() function call, and finally the fast interrupts are
enabled when Enable_Fast_Interrupts() is executed.
In the main() application loop, the program waits for the release
of the semaphore sem that was attached earlier. At this time, the
keyboard handler has collected a buffer of data and has detected the
input of an ‘=’. Also, the decode has been completed so that it is
possible to execute puts(a) to send the contents of the buffer to
the serial port. After the data are written to the output, to continue
operation, it is necessary to reattach the original semaphore if it is
available and proceed. This particular program will remain in the
inner loop forever reading inputs from the keyboard and outputting
them to the serial port whenever an ‘=’ button is depressed.
Usually at this point, a single listing of the whole program is
included in the text. It is a duplicate of the various smaller segments
shown above. Here I will refer to the program listing that is contained
on the CD-ROM. It can be found under the directory chapter8
and has the name kbinit.c.

Integrating Keyboard and Clock

The next piece of code will integrate the keyboard with the clock
developed earlier. The purpose of this program is to show the ease of
integrating these two programs and the use of more than one interrupt
simultaneously with the interrupt handler developed earlier. The main
change in the clock program will be to alter the reset_time()
function. This new function will receive inputs from the keypad. The
code developed in the previous section can be used, but it will have
to be altered significantly to be of use in this program. Here, we will
want to set up the keyboard input to interrupt when any key is
depressed and send a flag to the executing program when one or two
appropriate keys have been depressed. Let us increase the minutes