viuavm

; Main function of the program, automatically invoked by the VM. ; It must be present in every executable file. ; Valid main functions are main/0, main/1 and main/2. ; .function: main/0 ; Allocate local register set. ; This is done explicitly by the callee because it is an implementation ; detail - if a newer version of the function requires fewer (or more) ; registers the code using it should not have to be recompiled. ; Also, when a module is reloaded the code using it can stay the same as ; long as the number and types of parameters of the function stay the same. allocate_registers %4 local

; Store text value in local register with index 1.
; The text instruction shares operand order with majority of
; other instructions:
;
;   <mnemonic> <target> <sources>...
;
text %1 local "Hello World!\n"

; Store integer value in local register 2.
; Use a 1 because it will be used to represent the standard output stream on
; UNIX-like systems.
integer %2 local 1

; Write "Hello World!" on standard output. The io_write instruction will
; create an I/O request that will be carried out asynchronously and
; immediately return control to the process.
io_write %3 local %2 local %1 local

; Wait for the completion of the I/O request. In this case, the timeout
; given is 1 second.
; Void register (signified by the use of 'void') is used to tell the
; instruction that the result of the I/O operation is not needed and may be
; discarded.
io_wait void %3 local 1s

; The finishing sequence of every program running on Viua.
;
; Register 0 is used to store return value of a function, and
; the assembler will enforce that it is set to integer 0 for main
; function.
izero %0 local
return

.end