All memory cells and registers have 32 bits.
Registers are named R0,R1,R2,R3,R4,R5,R6,R7,...
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:
|<Label>:||mem||n||reserves n memory addresses|
|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|
addresses and set them to the correspondent characters ASCII
codes. The characters cannot be whitespaces: use
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.
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.
[<Label>:] Operation <Operand1> <Operand2>
Label is any string of letters or digits; if exists, must begin in the first column of a line
A line beginning with # will be ignored by the parser; so it can be used to write comments of the program
|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|
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:
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
Some Apoo programs can be found here
Rogério Reis,Nelma Moreira 2008-03-14