Page 428 - Programming Microcontrollers in C

Handling Interrupts 413

The next three functions can be used to send and receive strings
through the serial port. To use puts(), you use a string argument.
This function will send characters from the string until it finds a zero
value in the string. The get string functions perform similar to the
standard fgets() function. The difference between gets() and
getse() is that getse() echoes the characters read in to the serial
output. Otherwise these two functions are identical. You pass gets()
two parameters. The first is a pointer to a character array and the second
is the dimension of this array. As characters are read into the program,
they are stored in the character array. The string input is terminated by
either a ‘\n’ or a ‘\r’ character. The input will also be terminated
when the input character string is one less than the size of the array size.
When termination is detected, the input is terminated with a character
zero, making the data a string. The return to the calling program will be
–1 in the event that the character array was completely filled. Otherwise,
the return is the number of characters entered into the character array.
The function gets() reads data from the serial port with the
getch() function. This input does not echo the data entered.
getse() uses the getchar() to read the data in. getchar()
always echoes the input data to the serial output.
The above routines were separated into a series of individual
functions, which were combined into an archive library file. This file
is found on the CDROM under the name libserio.a. This file
can be linked during the linking operation like any other library file.

Handling Interrupts
All of the onboard peripherals found on the MMC2001 that need
access to interrupts are set up to use the core processor Auto Vector
capability. Shown in Table 8-1 is a copy of the interrupt vector table.
The vector table is placed at a location called the VBA, Vector Base
Address, when the chip is initialized. You will note that the table is
0x200, two hundred hex bytes, long. The vector numbers are
consecutive. The vector addresses move in steps of 4 and are usually
dealt with as hexadecimal values. This table must be filled in some
way when the program is initialized. Each vector will contain the address
of the function executed when the corresponding exception occurs.
Most of these vectors are self-explanatory. Of import here is the Fast
Interrupt Autovector location. Note that the offset of this vector is 0x2c.