Texas Instruments TMS34010 Reference Guide

Runtime Environment - Function Structure and Calling Conventions
3) It pushes the arguments on the program stack in reverse order (pushes
the rightmost declared argument first and pushes the leftmost declared
argument last).
If the called function does not have any arguments, the
canc. iiiu~t iivt jJ ... :;h ~~'i. !f th~ ~~lIed function expects one or more
arguments, the
caller must push at least one argument. The caller
generates the following code when it pushes the arguments:
MOVE @-arg3, *STK+, 1
MOVE @_arg2, *STK+, 1
MOVE @_argl, *STK+, 1
All integer types that are passed as arguments are widened to 32-bit in-
tegers. All floating-point arguments are converted to double-precision
values. Structures
are rounded up to the next word boundary.
4) If the called function returns a structure, the caller pushes the address
of the structure onto the program stack. (For more information about
functions that return structures, see Section 5.3.5.)
5) It calls the function by generating the following instruction:
CALLA -f
Note that within a called function, FS1 must equal 32.
The
called function restores the program stack pointer (effectively popping the
arguments), so there is no need for the calling function to perform any cleanup
after the
function call.
5.3.2 Responsibilities of a Called Function
A called function must perform the following tasks. The steps below show
examples of the code that the compiler might generate for a particular step.
1) If the function modifies any registers, it saves them on the system stack.
If it uses the FP, it must save it with the other registers. If the called
function must save multiple registers on the system stack, it can use the
M
MTM instruction as shown below:
MMTM SP, AS, A7, FP
It is not necessary to save register A8 or the status register. Note that
the C compiler doesn't use registers 80-814 so that assembly-language
functions can use them.
2) It executes the code for the function.
3) If the function returns an integer or a pointer, it returns the value in reg-
ister A8;
for example,
MOVE @result, A8, 1
If the function returns a double or a float, then the caller has allocated
space on the program stack for the return value; the called function co-
pies the value into that space. If the function returns a structure, see
Section 5.3.5.
4) It restores the caller's environment.
a) If the function has arguments or returns a float or a double, it must
restore the
caller's stack. To do this, it moves the value out of the
system stack
to the program stack pointer (register A14). The STK
is stored on the system stack below the saved registers and the old
5-9

Texas Instruments TMS34010 Specifications

General

Brand	Texas Instruments
Model	TMS34010
Category	Computer Hardware
Language	English