Difference between revisions of "Motorola 68000"

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=== The Motorola 68k processor  ===
 
=== The Motorola 68k processor  ===
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The Motorola 68k processor...  
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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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Note:  Assigment direction is source,dest instead of dest,source !!!
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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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=== Registers ===
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Note: The assigment direction is source,dest instead of dest,source !!!
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To be added.
 
  
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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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* Emulator(s): -. Make sure to use the original TOS 1.62 Image for best compatibility.
 
  
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=== Compiling to a TOS image ===
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* A7 - 32-bit Stack-Address Register
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Vasm -Ftos source.s -o source.tos
 
  
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=== Video diplay ===
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==== Instructions timing ====
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The Atari ST has a linear 320x200x4bit address space, which each nibble representing a color index 0..F from the palette.
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The number of cycles for each instruction is different depending of processor model in M68K family.
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: http://oldwww.nvg.ntnu.no/amiga/MC680x0_Sections/mc68000timing.HTML
  
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To be added soon.
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== Size considerations ==
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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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=== Setting a palette ===
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* Moving/Calculating Register from/to registers - 2 bytes
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Here is some code that will help you setup a palette
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* Moving/Calculating with byte or word values - 4 bytes
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* Moving/Calculating with long values - 6 bytes
  
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<syntaxhighlight lang="">
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Shorter variants:
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pea palette(pc)
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* moveq #value, reg : 2 bytes - Moves a values -128...127 to a register
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move.w #6,-(sp)
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* addq #value, reg : 2 bytes - Adds a values 0..8 to a register
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trap #14
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* subq #value, reg : 2 bytes - Subtracts a values 0..8 from a register
  
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; Palette data
 
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palette:
 
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dc.w $000,$100,$200,$311,$422,$533,$644,$755
 
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dc.w $575,$464,$353,$242,$131,$020,$010,$000
 
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</syntaxhighlight>
 
  
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=== Getting something on screen ===
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== Generic 68K sinus table generator ==
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Here is a bit of code to get you started:
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Here is a fairly generic 68k sinus table generator (16 bytes on Atari ST) as well as a 10-byte zigzag generator.
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* [https://demozoo.org/productions/310191/ Singen68k]
  
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<syntaxhighlight lang="">
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== Resources ==
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;-----------------------
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* [http://www.beycan.net/eklenen/M68000_Instruction_Set.pdf M68000 Instruction Set]
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; Line-A Initialization
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* [http://www.easy68k.com/ EASy68K Editor/Assembler/Simulator for the 68000]
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;-----------------------
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* [http://www.easy68k.com/paulrsm/index.html Various Motorola 68k resources]
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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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== Motorola M68K Platforms ==
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; For X&Y
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*'''[[Atari ST]]''' - Atari ST Sizecoding information
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;---------
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*'''[[Atari Jaguar]]''' - Atari Jaguar Sizecoding information
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frameloop:
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*'''[[Commodore Amiga]]''' - Commodore Amiga Sizecoding information
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move.w #200-1,d7 ; y
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*'''[[Spectrum QL]]''' - Spectrum QL information
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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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</syntaxhighlight>
 
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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.
 
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=== Additional Resources ===
 
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Sizecoding on the Atari ST is not very huge yet, so resources are sparse.
 
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* Spkr's Github: to be added
 

Latest revision as of 12:51, 8 April 2024

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


Generic 68K sinus table generator

Here is a fairly generic 68k sinus table generator (16 bytes on Atari ST) as well as a 10-byte zigzag generator.

Resources

Motorola M68K Platforms

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