Difference between revisions of "Motorola 68000"

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== Introduction ==
 
== Introduction ==
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Wanting to start sizecoding on a 6502 platform in this day and age can be tough.  
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Wanting to start sizecoding on a Motorola 68k platform in this day and age can be tough.  
  
 
So here is a bit of help to get you started:
 
So here is a bit of help to get you started:
  
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=== The 6502 processor  ===
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=== The Motorola 68k processor  ===
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The 6502 processor can be seen as the 8bit micro ARM chip.
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The Motorola 68k processor is a 16-bit Big-Endian format processor, using 32-bit register and addresses.
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It has only has 3 registers (Accumilator, IX and IY registers) and only a handful of instructions to work with.
 
  
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=== Registers ===
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This means that instruction sizes on average are either 2 or 4 bytes each, and 6 bytes for longword / 32-bit instructions.
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To be added.
 
  
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=== Zero page ===
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Note: The assigment direction is source,dest instead of dest,source !!!
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When using the 6502 for sizecoding, you'll mostly be working from zeropage
 
  
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== Atari ST ==
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==== Registers ====
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The Atari ST systems consists of the M68k system with custom hardware for graphics and sound.
 
  
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=== Setting up ===
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* D0..D7 - 8 x 32 bit General Purpose Registers
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Setting up your development platform for the Atari ST systems is quite easy, first get the following tools:
 
  
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* Assembler: VASM - This assembler is able to assemble directly to a TOS image
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* A0..A6 - 7 x 32 bit Address Registers
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https://sourceforge.net/projects/sjasmplus/
 
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* Emulator(s): -. Make sure to use the original TOS 1.62 Image for best compatibility.
 
  
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* A7 - 32-bit Stack-Address Register
  
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=== Compiling to a TOS image ===
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==== Instructions timing ====
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Vasm -Ftos source.s -o source.tos
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The number of cycles for each instruction is different depending of processor model in M68K family.
 +
: http://oldwww.nvg.ntnu.no/amiga/MC680x0_Sections/mc68000timing.HTML
  
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=== Video diplay ===
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== Size considerations ==
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Video display on the Atari 8bit systems use the TIA chip, it has the following video modes:
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Here are some general rule of thumbs when it comes to size consideration when programming the M68000
  
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To be added soon.
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* Moving/Calculating Register from/to registers - 2 bytes
 +
* Moving/Calculating with byte or word values - 4 bytes
 +
* Moving/Calculating with long values - 6 bytes
  
 +
Shorter variants:
 +
* moveq #value, reg : 2 bytes - Moves a values -128...127 to a register
 +
* addq #value, reg : 2 bytes - Adds a values 0..8 to a register
 +
* subq #value, reg : 2 bytes - Subtracts a values 0..8 from a register
  
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=== Setting a palette ===
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== Resources ==
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pea palette(pc)
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* [http://www.beycan.net/eklenen/M68000_Instruction_Set.pdf M68000 Instruction Set]
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move.w #6,-(sp)
 
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trap #14
 
  
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; Palette data
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== Motorola M68K Platforms ==
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palette:
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*'''[[Atari ST]]''' - Atari ST Sizecoding information
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dc.w $000,$100,$200,$311,$422,$533,$644,$755
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*'''[[Atari Jaguar]]''' - Atari Jaguar Sizecoding information
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dc.w $575,$464,$353,$242,$131,$020,$010,$000
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*'''[[Commodore Amiga]]''' - Commodore Amiga Sizecoding information
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=== Getting something on screen ===
 
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Here is a bit of code to get you started:
 
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;-----------------------
 
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; Line-A Initialization
 
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;-----------------------
 
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; After calling this function, data register D0 and address register A0 point to a table ; with the starting address of the Line A variables.
 
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; Address register A1 points to a table with the starting addresses for the three system ; font headers,
 
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; and address register A2 points to a table that specifies the starting addresses of the; 15 Line A opcodes. There's no parameter required for this function, so all you have
 
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; to do is call the word opcode label that you specified for the $A000 (Initialize)
 
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; function.
 
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dc.w $A000
 
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movem.l (a0),a1-a4 ; A3=INTIN, A4=PTSIN
 
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;---------
 
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; For X&Y
 
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;---------
 
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frameloop:
 
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move.w #200-1,d7 ; y
 
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yLoop:
 
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move.w #320-1,d6 ; x
 
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xLoop:
 
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; Putpixel
 
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put_pixel:
 
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move.b d6,d0 ; d0=x
 
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eor d7,d0 ; d0=x^y
 
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lsr.b #2,d0 ; d0>>=4
 
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and #42,d0 ; d0&42
 
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move.w d0,(a3) ; a3=color(d0)
 
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movem.w d6/d7,(a4) ; a4=x,y`
 
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dc.w $A001 ; put pixel command
 
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dbra d6,xLoop ; decrease and branch
 
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    dbra d7,yLoop
 
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; Wait loop
 
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bra frameloop ; .s *
 
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=== Sound ===
 
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The Atari ST systems use the YM8192 chip to generate sound.
 
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To be added soon.
 
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=== Make some noise ===
 
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To be added soon.
 

Revision as of 07:05, 20 June 2022

Introduction

Wanting to start sizecoding on a Motorola 68k platform in this day and age can be tough.

So here is a bit of help to get you started:

The Motorola 68k processor

The Motorola 68k processor is a 16-bit Big-Endian format processor, using 32-bit register and addresses.

This means that instruction sizes on average are either 2 or 4 bytes each, and 6 bytes for longword / 32-bit instructions.

Note: The assigment direction is source,dest instead of dest,source !!!

Registers

  • D0..D7 - 8 x 32 bit General Purpose Registers
  • A0..A6 - 7 x 32 bit Address Registers
  • A7 - 32-bit Stack-Address Register

Instructions timing

The number of cycles for each instruction is different depending of processor model in M68K family.

http://oldwww.nvg.ntnu.no/amiga/MC680x0_Sections/mc68000timing.HTML

Size considerations

Here are some general rule of thumbs when it comes to size consideration when programming the M68000

  • Moving/Calculating Register from/to registers - 2 bytes
  • Moving/Calculating with byte or word values - 4 bytes
  • Moving/Calculating with long values - 6 bytes

Shorter variants:

  • moveq #value, reg : 2 bytes - Moves a values -128...127 to a register
  • addq #value, reg : 2 bytes - Adds a values 0..8 to a register
  • subq #value, reg : 2 bytes - Subtracts a values 0..8 from a register

Resources

Motorola M68K Platforms

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