Apoo assembly language

Apoo has a set of general purpose registers (32 by default), a data memory area, a program memory area, a system stack and a program counter register.

All memory cells and registers have 32 bits.

Registers are named R0,R1,R2,R3,R4,R5,R6,R7,...

Memory Management

The size of the RAM is predefined (e.g. 1K) and divided into two areas: static memory and system stack. The static memory, begins at address 0 and it is allocated when a Apoo program is loaded. Static memory cells can be reserved in in two ways, using the following pseudo-instructions:

Pseudo-instructions

			Meaning
<Label>:	mem	n	reserves n memory addresses
<Label>:	const	n1
	const	n2	contents of memory address Label is n1, of Label+1 is n2
		....	ni can be a character 'c'.
<Label>:	equ	n	Allows a symbolic name for a number
<Label>:	string	"seqNWSCharacteres"	Allocates memory addresses and set them to the correspondent characters ASCII codes. The characters cannot be whitespaces: use \s for space, \t for tab and \n for newline.

Label is any string beginning with a letter and containing only letters and digits with the exception of legal register names. If exists, must begin in the first column of a line

NOTE: Every memory address refered, must have been reserved by one of the previous pseudo-instructions.

E.g. the instruction load 3 R2, will cause an Out of Memory error, if at least mem 3 or three const pseudo-instructions were not given... If a equ value is used as a memory address, that address must be already reserved or be a known memory-mapped instruction. The string argument must be quoted and is converted to a sequence of ascii codes ending with 0.

System Stack

The system stack occupies the rest of the RAM (growing for higher addresses). Since Apoo version 2.2 it can be used in an advanced way to implement activation records (see section 3.2). However in can be used in a simpler way to implement subroutines. We can only push a value to the Stack and pop a value from it (the one in the top of the Stack). It is used by the instructions jsr and rtn.

It can be manipulated by means of the push and pop instructions.

Versions prior to 2.2 uses the same syntax but diferent graphical interface for the visualization of the System Stack.

Instruction form

[<Label>:] Operation <Operand1> <Operand2>

Label is any string of letters or digits; if exists, must begin in the first column of a line

Comments

A line beginning with # will be ignored by the parser; so it can be used to write comments of the program

Basic Instruction Set

Operation	Operand1	Operand2	Meanning
load	Mem	Ri	loads contents of memory address Mem into register Ri; Mem can be a label
loadn	Num	Ri	loads number Num into register Ri; Num can be a label
loadi	Ri	Rj	loads contents of memory which address is the contents of Ri into Rj (indirect load)
store	Ri	Mem	stores contents of Ri at memory address Mem; Mem can be a label
storer	Ri	Rj	stores contents of Ri into Rj
storei	Ri	Rj	stores contents of Ri into at memory address, which is the contents of Rj
add	Ri	Rj	add contents of register Ri to contents of register Rj, and stores into Rj (Rj=Ri+Rj)
sub	Ri	Rj	subtracts contents of register Rj from contents of register Rj and stores into Rj (Rj=Ri-Rj)
mul	Ri	Rj	multiplies contents of register Ri and contents of register Rj, and stores into Rj (Rj=Ri*Rj)
div	Ri	Rj	stores into Rj the quotient of integer division of contents register Ri by the contents of register Rj, and stores into Rj (Rj=Ri/Rj)
mod	Ri	Rj	stores into Rj the rest of integer division of contents of register Ri by the contents of register Rj, and stores into Rj (Rj=Ri%Rj)
zero	Ri		the contents of Ri becomes 0 (Ri=0)
inc	Ri		increments by 1 the contents of Ri
dec	Ri		decrements by 1 the contents of Ri
jump	Addr		jumps to instruction address Addr; Addr can be a Label
jzero	Ri	Addr	jumps to instruction address Addr, if contents of Ri is zero; Addr can be a Label
jpos	Ri	Addr	jumps to instruction address Addr, if contents of Ri is positiv; Addr can be a Label
jneg	Ri	Addr	jumps to instruction address Addr, if contents of Ri is negativ
jnzero	Ri	Addr	jumps to instruction address Addr, if contents of Ri is different from zero; Addr can be a Label
jsr	Addr		pushes the PC into the stack and jumps to instruction address Addr
rtn			pops an address from the stack into the PC
push	Ri		pushes the contents of Ri into the system stack
pop	Ri		pops at element from the system stack into Ri
halt			stops execution; Every program must have this instruction in order to end properly; otherwise an 'Out of Program' error will occur

Memory- mapped instructions

Apoo allows the configuration of a set of memory positions for special purposes. The memory values and its functionality are given as a parameter of the Apoo virtual machine. The default values allow the simulation of input/output:

Memory Position	Load	Store
50000	load 50000 Ri loads 0 in Ri	store Ri 50000 writes the character which ascii code is Ri%256 in the Output Window (in graphical interface) or in stdout, in text mode.
50001	load 50001 Ri reads an integer and stores it in Ri	store Ri 50001 writes the contents of Ri as an integer
50010	load 50010 Ri loads 0 in Ri	store Ri 50010 writes a CR in the Output Window (in graphical interface) or in stdout, in text mode.

Here is an example:

	loadn	97	R0
	store	R0	50000
	store 	R0	50010
	store	R0	50001
	store	R0	50010
	load	50001	R0
	loadn	5	R1
	add	R0	R1
	store	R0	50001
	store 	R0	50010
	halt

Examples

Some Apoo programs can be found here