ZBasic Language Reference
130
ZBasic Microcontrollers
Program Element Prefixes
Element
Prefix (if Public)
Prefix (if Private)
subroutine or function
zf_
mzf_
variable
zv_
mzv_
structure
zs_
mzs_
structure member
zm_
zm_
parameter
zp_
function return value
zr_
Accessing ZBasic program elements in inline assembly code is possible but is more complicated partly
due to issues regarding the register allocation, code generation and optimization stragegies employed by
the compiler that translates the generated C code to native object code, discussion of which is beyond the
scope of this document. That said, here is a simple example using inline assembly code.
Public b as Byte
#c
char ch;
#endc
Sub Main()
b = 5
#asm
; save the registers used
push r30
push r31
push r24
; load the address of the variable
ldi r30, lo8(zv_b)
ldi r31, hi8(zv_b)
; load the variable's value and save it
ld r24, Z
sts ch, r24
; restore the registers used
pop r24
pop r31
pop r30
#endasm
End Sub
It is important to note that inline assembly code must avoid altering certain registers that the compiler
expects to remain unchanged. (The same is true, of course, of any assembly language code.) The code
in the example above saves registers that it uses on the stack before using them and then restores their
values afterward. There is a mechanism to inform the compiler as to which registers are altered in the
inline assembly code thus allowing the compiler to automatically perform the save/restore if necessary.
Discussion of that mechanism is an advanced topic that is beyond the scope of this document.
6.2 Defining and Using External Subroutines, Functions and Variables
For the native mode devices you may include .c files (C language), .S files (AVR assembly language), .o
files (AVR object code) and .a files (AVR object code archives) in your project. When processing the
component files of a project, the ZBasic compiler will note the presence of these special files but will
otherwise ignore them except for including them in the final build phase. In order to invoke subroutines
and functions contained in these special files, you must declare them so the ZBasic compiler knows how
to check for invocation syntax errors and how to generate code to invoke them.
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