(c) sashz sashz@pdaXrom.org, 2020-2021

MICROCPU - 16-bit RISC CPU (Version 2)

Registers
Address modes
Instructions
MicroAssembler
Bootloader
- Bootloader options
Lattice Diamond programmer and ftdi jtag dual channel board
Microcontroller with Lattice MachXO2-1200 microboard
Microcomputer with Lattice MachXO2-1200

Registers

The processor has eight 16-bit registers. The register 0 (PC) using as program counter.

Numeric	Name	Alias
0	R0	PC
1	R1	SP
2	R2	LR
3	R3	V0
4	R4	V1
5	R5	V2
6	R6	V3
7	R7	V4

Each register has high byte and low byte:

15 14 13 12 11 10 09 08	07 06 05 04 03 02 01 00
HIGH BYTE	LOW BYTE

Top

Address modes

The processor has 5 addressing modes that can be used by the programmer:

Register
Immediate
Immediate indexed
Register indexed
Relative

Top

Instructions

Machine instructions generally fall into three categories: data movement, arithmetic/logic, control-flow and cpu modes control. We use the following notation:

Notation	Description
`<dst>`	Any destination register
`<src>`	Any source register
`<imm>`	8-bit immediate
`<imm16>`	16-bit immediate
`<idx>`	Any register or 4-bit unsigned immediate
`<arg1>`	Any register
`<arg2>`	Any register or 4-bit unsigned immediate
`<rel>`	11-bit signed immediate

Top

Data Movement Instructions

Instruction		Description
`LDRL <dst>, <src>, <idx>`	`RL<dst> = M[R<src> + idx]`	Load low byte from source address + index
`STRL <dst>, <src>, <idx>`	`M[R<src> + idx] = RL<dst>`	Store low byte to source address + index
`LDR <dst>, <src>, <idx>`	`R<dst> = M[R<src> + idx]`	Load register (2 bytes) from source address + index
`STR <dst>, <src>, <idx>`	`M[R<src> + idx] = R<dst>`	Store register (2 bytes) to source address + index
`SETL <dst>, <imm>`	`RL<dst> = imm`	Copy low byte from constant
`SETH <dst>, <imm>`	`RH<dst> = imm`	Copy high byte from constant
`MOVL <dst>, <src>`	`RL<dst> = RL<src>`	Copy source low byte to destination low byte
`MOVH <dst>, <src>`	`RH<dst> = RL<src>`	Copy source low byte to destination high byte
`MOV <dst>, <src>`	`R<dst> = R<src>`	Copy data from source to destination register

Little endian byte order using for LDR and STR.

Examples:

    SETL V0, 0
    SETH V0, $10
    LDRL V1, V0, 0
    SETL V2, 1
    SETH V2, 0
    STR  V1, V0, V2
    MOV V3, V2

Top

Arithmetic and Logic Instructions

Instruction		Description
`ADD <dst>, <arg1>, <arg2>`	`<dst> = <arg1> + <arg2>`	Add
`SUB <dst>, <arg1>, <arg2>`	`<dst> = <arg1> - <arg2>`	Subtract
`SHL <dst>, <arg1>, <arg2>`	`<dst> = <arg1> << <arg2>`	Logic shift left
`SHR <dst>, <arg1>, <arg2>`	`<dst> = <arg1> >> <arg2>`	Logic shift right
`AND <dst>, <arg1>, <arg2>`	`<dst> = <arg1> & <arg2>`	And
`OR <dst>, <arg1>, <arg2>`	`<dst> = <arg1> \| <arg2>`	Or
`INV <dst>, <arg1>`	`<dst> = ~<arg1>`	Inversion
`XOR <dst>, <arg1>, <arg2>`	`<dst> = <arg1> ^ <arg2>`	Exclusive Or
`SXT <dst>, <arg1>`	`<dst> = sign <arg1>`	Sign extend

Examples:

    ADD V0, V1, V2
    SUB V0, V2, V1
    SHR V0, V0, 1
    SXT V1, V1

Top

Control Flow Instructions

Instruction		Description
`B <rel>`	`PC = PC + <rel>`	Branch
`EQ <arg1>,<arg2>`	`PC = PC + (<arg1> == <arg2>) ? 2 : 0`	Skip next command if arg1 and arg2 are equal
`NE <arg1>,<arg2>`	`PC = PC + (<arg1> != <arg2>) ? 2 : 0`	Skip next command if arg1 and arg2 are not equal
`LT <arg1>,<arg2>`	`PC = PC + (<arg1> < <arg2>) ? 2 : 0`	Skip next command if arg1 is less than arg2 (signed)
`GE <arg1>,<arg2>`	`PC = PC + (<arg1> >= <arg2>) ? 2 : 0`	Skip next command if arg1 is greater then arg2 or equal (signed)
`LTU <arg1>,<arg2>`	`PC = PC + (<arg1> < <arg2>) ? 2 : 0`	Skip next command if arg1 is less than arg2 (unsigned)
`GEU <arg1>,<arg2>`	`PC = PC + (<arg1> >= <arg2>) ? 2 : 0`	Skip next command if arg1 is greater then arg2 or equal (unsigned)
`BTC <arg1>,<arg2>`	`PC = PC + (<arg1> & <arg2>) ? 2 : 0`	Skip next command if arg1 AND arg2 result is zero
`BTS <arg1>,<arg2>`	`PC = PC + (<arg1> & <arg2>) ? 2 : 0`	Skip next command if arg1 AND arg2 result is not zero

Examples:

    B	start
    EQ	V0, V1
    B	not_the_same
    B	the same

Top

CPU Modes Control

Instruction		Description
`SWS`	`UPC = PC; PC = VEC_SUPER`	Switch to superuser mode
`SWU`	`PC = UPC`	Return to user mode
`GETS <dst>`	`<dst> = <User PC>`	Get user programm counter
`SETS <src>`	`<User PC> = <src>`	Set user programm counter

Examples:

    ORG	$0
    B	start
    B	su
    ...
su  SUB SP, SP, 2
    PUSH V0
    GETS V0
    ...
    PUTS V0
    POP  V0
    ADD SP, SP, 2
    SWU
    ...
ini SWS
    ...

Top

Interrupts

The system supports two interrupts - the CPU command to switch to superuser mode (SWS command) and peripheral interrupt (external signal). Both interrupts cause a jump to address $0002 while saving the interrupted address in a special register, which is available for modification using the GETS and PUTS commands. Exit from the interrupt mode is performed using the SWU command. Until the end of the execution of the mode, other interrupts are prohibited.

Top

MicroAssembler

Assembler has support for macros, procedures. Since the processor has a limited number of instructions, some instructions can be implemented as macros.

Top

Assembler directives

Directive	Description
`<symbol> EQU <exp>`	Set a symbol equal to an expression
`DB <imm>[,<imm>...]`	Define constant byte(s)
`DW <imm16>[,<imm16>...]`	Define constant word(s)
`DS <imm16>[,<imm>]`	Reserves num bytes of space and initializes them to val (optional, defaul 0).
`ALIGN <imm>`	Align address to num bits
`ORG <imm16>`	Set location address counter
`INCLUDE <file name>`	Include external source file
`CHKSUM`	Insert constant word to binary to sum all words as $FFFF

Examples:

    INCLUDE functions.inc
CONST_ONE EQU 1
CONST_TWO EQU 2
    ORG $100
    DB 1, $2, $3, 4, 5
    DB "Hello, World", 0
    DB 'About'
    DW $1234, 8192, 0
    DS 32
    DS 64,$FF
    ALIGN 4

Top

Accembler macro definition

Directive	Description
`MACRO <name>`	Start macro
`ENDM`	End macro

macro parameters start with # and are numbered from 1.

Example:

    MACRO SET
    SETH	#1, /#2
    SETL	#1, #2
    ENDM

    SET V0, $1234

Top

Assembler procedures

Directive	Description
`<label> PROC`	Start procedure
`GLOBAL <label>[,<label>...]`	Add local procedure label as global
`ENDP`	End procedure

Example:

get_one PROC
    SET V0, 1
    ADD PC, LR, 3
    ENDP
	
get_1 PROC
    GLOBAL get_2
    SET V0, 1
return ADD PC, LR, 3
get_2 SET V0, 2
    B return
    ENDP

Top