Zilog ZUSBOPTS - Manual (Page 203)

UM017105-0511 Calling Assembly Functions from C
Zilog Developer Studio II – ZNEO™
User Manual
175
Argument Locations
The assembly function assigns the location of the arguments following the C calling con-
ventions as described in the
Calling Conventions section on page 172. For example, if you
are using the following C prototype:
void myfunc(short arga, long argb, short *argc, char argd, int
arge, int argf, char argg, long *argh, int argi)
then the location of the arguments are:
arga : R1
argb : R2
argc : R3
argd : R4
arge : R5
argf : R6
argg : R7
The remaining arguments are on stack, and their offsets from Stack Pointer (SP, R15) at
the entry point of assembly function are:
argh : - 4(SP)
argi : - 8(SP)
The corresponding offsets from Frame Pointer (FP, R14) after a Link #0 instruction are:
argh : - 8(FP)
argi : - 12(FP)
Return Values
The assembly function returns the value in the location as specified by the C calling con-
vention as described in
Calling Conventions on page 172.
For example, if you are using the following C prototype:
long myfunc(short arga, long argb, short *argc)
then the assembly function returns the long value in register R0.