Zilog Z8F0130 - Manual (Page 241)

UM013037-1212 Function Call Mechanism: Static Frame
Zilog Developer Studio II – Z8 Encore!
User Manual
217
1. For a non- varargs function, load parameters into the corresponding static locations
for the function. For a varargs function, a dynamic frame is always used, and all
parameters are pushed on the stack in reverse order.
2. Then call the function. The call instruction pushes the return address on the top of the
stack.
3. On return from the function, the return address is automatically popped from the stack
by the ret instruction.

The called function performs the following tasks:
1. If the called function is a monitor function only, push the existing value of the inter-
rupt control register IRQCTL on the stack and disable interrupts.
2. Push the frame pointer onto the stack and set the frame pointer to the current value of
the stack pointer.
3. Execute the code for the function.
4. If the function returns a scalar value, place it in the return registers. For functions
returning an aggregate, see the Special Cases section on page 220.
5. Set the stack pointer to the current value of the frame pointer and restore the frame
pointer from the stack.
6. If the called function is a monitor function only, restore the interrupt control register
IRQCTL from the stack.
7. Return.

For a static frame function, steps 2 and 5 are only done if the –debug (Debug) or

–reduceopt (Limit Optimizations for Easier Debugging) option is selected. All registers,
other than the return register, are considered as caller save, that is, they are saved and
restored by the caller function. The flag register is not saved and restored by the caller
function.
The preceding function call mechanism is a static call mechanism. The structure of a static
call frame is described in the
Structure of a Static Call Frame section on page 217.
Structure of a Static Call Frame
For the static frame function fun , the local variables and parameters are allocated in a
frame labeled _f_fun for a large model and _n_fun for a small model. The parameters
are numbered from left to right and are named as _x_ fun , in which x indicates the number
associated with the parameter. In the following example, _0_fun represents the left-most
parameter ( ch1 ), and _1_fun represents the next parameter ( ch2 ).