Zilog EZ80F916 - Manual (Page 156)

UM014423-0607 Using the ANSI C-Compiler
ZiLOG Developer Studio II
eZ80Acclaim! ® User Manual
136
a value. Because an interrupt handler is not called from another function but vectored to
by the hardware, you cannot pass parameters to it. Interrupt routines can, however, access
global variables or static variables. The compiler issues a warning if it detects an interrupt
routine with arguments.
The compiler stores the machine state at the beginning of these functions and restores the
machine state at the end of these functions. The
interrupt
and
nested_interrupt
pragma
s are handled differently in the compiler. You should use
#pragma interrupt
for all interrupt handlers if your application does not make use of nested interrupts; other-
wise, use
#pragma nested_interrupt
for all interrupt handlers. It is important to use
either
interrupt
or
nested_interrupt
consistently throughout your application.
Specifically, the (non-nested)
interrupt
function executes an
EXX
instruction that pre-
serves all the current registers upon entry to the function and an
EXX
instruction to restore
the registers at the function exit. On the other hand,
nested_interrupt
does not use the
alternate registers and instead pushes registers on the stack based on their use in the func-
tion. In either case, the compiler uses the reti instruction to return from these functions.
For example:
void interrupt isr_timer0(void) /* For non-nested interrupt use model */
{}
or
void nested_interrupt isr_timer0(void) /* For nested interrupt use model */
{}
or
#pragma interrupt /* For non-nested interrupt use model */
void isr_timer0(void)
{}
or
#pragma nested_interrupt /* For nested interrupt use model */
void isr_timer0(void)
{}
If you want the compiler to use the
retn
instruction to return from the interrupt, use
#pragma nmi_interrupt
. For example:
#pragma nmi_interrupt /* ISR for non maskable interrupt */
void isr_nmi(void)
{}
Interrupt Vector Setup
The compiler provides the
_set_vector
function for interrupt vector setup. This func-
tion can be used to specify the address of an interrupt handler for an interrupt vector. The
_set_vector
function works by dynamically reading the base of the vector table and
placing the address of the interrupt handler in it.