Superogue: Created page with "== Atari Lynx == The Atari Lynx consists of the 65C02 with custom hardware for graphics and sound.
If you come from Atari 8bit or Apple, there are no illegal opcodes anymo..."

2022-03-10T13:15:09Z

Created page with "== Atari Lynx == The Atari Lynx consists of the 65C02 with custom hardware for graphics and sound. If you come from Atari 8bit or Apple, there are no illegal opcodes anymo..."

New page

== Atari Lynx ==
The Atari Lynx consists of the 65C02 with custom hardware for graphics and sound. 
If you come from Atari 8bit or Apple, there are no illegal opcodes anymore like lax, but a lot new nice opcodes like stz. :-)

=== Setting up ===
Setting up your development platform for the Atari Lynx:

* Assembler:
Below size coding examples use [https://github.com/42Bastian/lyxass Lyxass] as assembler and are using the in-official DevKit [https://github.com/42Bastian/new_bll new_bll]. 
But any other 6502 assembler is suitable. Best if it can assemble the extra opcodes of the 65C02 (like BBRx or RMBx).

* Encryption
The Lynx boot ROM will decrypt the "boot sector" of a Lynx card image. It is done in chunks of 50bytes. Maximum are 5 chunks, hence the limit of a "boot sector" is 250 bytes, but the last byte must be zero.

* Emulator(s):
Currently Felix is the most accurate Emulator, though only running yet on Windows platform. 
It is currently available via [https://github.com/laoo/Felix GitHub].

* Hardware:
If you want to run the code on a real Lynx, you should have a SD card for the Lynx (AgaCard, LynxGD) and also a USB<->Serial adapter.

=== Initial values ===
After the boot-rom has decrypted the boot-sector, some things are pre-defined:
* CPU Registers:
A = 0
X = 0
Y = 2
P = undefined
S = undefined

* Zero page

$00 - 0
$01 - 0
$02 - 0

* Main

Main memory is cleared to zero despite a $5000..%$50aa where decryption code is placed.

* Bank switching

ROM, Mikey and Suzy are mapped, Vector table is ROM.

* Suzy
The sprite engine is not setup.

=== Video display ===
The Lynx display is 160x102 pixels which are linear organized as 4 bit per pixel. Hence the screen is little less than 8K.
The pixel value is a pointer to the color look up table.
The Lynx can display black and 4095 colors. The color table is split up into a green and an blue-red part (so not RGB but GBR).

==== Getting something on screen ====
After the ROM has deciphered the boot sector the display memory is at $2000, background color (that is pen 0) is black, all other entries are $f despite entry 14 which is also 0.

So to fill the screen simply do:
<pre>
lda #$ff
ldx #0
ldy #$20 ; round(160*102/2/256)
loop:
sta $2000,x
inx
bne loop
inc loop+2 ; Self modify
dey
bne loop
</pre>

=== Tips 'n' tricks ===
A nice trick with the new opcodes to limit a counter:
* 6502
lda counter ; 2
inc ; 1
and #3 ; 2
sta counter ; 2 = 7 bytes

* 65C02
inc counter ; 2
rmb2 counter ; 2 => 4 bytes

Set a counter (previously 0) to a power-of-two (here 32)

* 6502
lda #32 ; 2
sta counter ; 2 => 4

* 65C02
smb5 counter ; 2

=== Sound ===
To be added soon.

==== Make some noise ====
To be added soon.

=== Additional Resources ===
*[https://www.monlynx.de/lynx/lynxdoc.html Hardware documentation]
*[https://github.com/42Bastian/lynx_hacking/tree/master/248b Size coding examples.]
*[https://github.com/42Bastian/lynx-encryption-tools Lynx encryption-tools]

Atari Lynx - Revision history

Superogue: Created page with "== Atari Lynx == The Atari Lynx consists of the 65C02 with custom hardware for graphics and sound. If you come from Atari 8bit or Apple, there are no illegal opcodes anymo..."

Superogue: Created page with "== Atari Lynx == The Atari Lynx consists of the 65C02 with custom hardware for graphics and sound.
If you come from Atari 8bit or Apple, there are no illegal opcodes anymo..."