┌────────────────────────────────────────────┐
│ Programming the ATI Technologies SVGA Chip │
└────────────────────────────────────────────┘
Written for the PC-GPE by Mark Feldman
e-mail address : u914097@student.canberra.edu.au
myndale@cairo.anu.edu.au
Please read the file SVGINTRO.TXT
(Graphics/SVGA/Intro PC-GPE menu option)
┌───────────────────────────────────────────┐
│ THIS FILE MAY NOT BE DISTRIBUTED │
│ SEPARATE TO THE ENTIRE PC-GPE COLLECTION. │
└───────────────────────────────────────────┘
┌────────────┬───────────────────────────────────────────────────────────────
│ Disclaimer │
└────────────┘
I assume no responsibility whatsoever for any effect that this file, the
information contained therein or the use thereof has on you, your sanity,
computer, spouse, children, pets or anything else related to you or your
existance. No warranty is provided nor implied with this information.
┌────────────────────────────────────┬───────────────────────────────────────
│ Locating the Extended Register Set │
└────────────────────────────────────┘
The ATI extended register set is based on the vga's index register scheme,
ie you write the value of the register you want to modify to Index Register
Port and write the actual data to the Data Port (the Data Port is one port
number higher than the Index Register Port). The value of the Index Register
for the ATI extended register set is stored in a word in BIOS ROM at
C000:0010. Apparently ATI want to change the value of this register in
future so they recommend you obtain it by reading the value at this memory
address.
┌──────────────────────────┬─────────────────────────────────────────────────
│ Identifying the ATI Chip │
└──────────────────────────┘
The ATI chip can be identified by checking the string in memory locations
C000:0031-003A for the following characters : 761295520
┌────────────────────────────┬───────────────────────────────────────────────
│ Identifying which ATI Chip │
└────────────────────────────┘
The first version of the ATI chip is the 18800. The second version is the
28800, which from a programming perspective is identical to the 18800-2.
The 18800 can be identified by it's lack of support for display mode
55h.
┌──────────────────────────────────────────┬─────────────────────────────────
│ Determining the ATI Chip Revision Number │
└──────────────────────────────────────────┘
The ATI chip revision number is stored at BIOS location C000:0043.
┌────────────────────────────┬───────────────────────────────────────────────
│ ATI Graphics Display Modes │
└────────────────────────────┘
┌───────────────────────────────────────────────┐
│ Mode Resolution Colors Chip │
├───────────────────────────────────────────────┤
│ 53h 800x600 16 18800 │
│ 54h 800x600 16 18800 │
│ 55h 1024x768 16 (planar) 18800-1 │
│ 61h 640x400 256 18800 │
│ 62h 640x480 256 18800 │
│ 63h 800x600 256 18800 │
│ 65h 1024x768 256 (packed) 18800 │
│ 67h 1024x768 4 ? │
└───────────────────────────────────────────────┘
┌────────────────────┬───────────────────────────────────────────────────────
│ ATI Display Memory │
└────────────────────┘
In the following examples the EXT variable is the extended register index
value obtained from reading the word at C000:0010.
The ATI supports both single and duel bank memory mapping. It supports 64K
byte pages, each of these can be mapped into the host address space.
Single or duel bank mode is selected by the E2B bit in register BE
Index : BEh at port EXT
Read/Write at port EXT + 1
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ 7 │ 6 │ 5 │ 4 │ 3 │ 2 │ 1 │ 0 │
└───┴───┴───┴───┴───┴───┴───┴───┘
│
└────────────── E2B 0 = Single Bank Mode
1 = Duel Bank Mode
Selecting a bank to write to in single bank mode is done by writing the bank
number to the Bank Select Register :
Index : B2h
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ 7 │ 6 │ 5 │ 4 │ 3 │ 2 │ 1 │ 0 │
└───┴───┴───┴───┴───┴───┴───┴───┘
└─────┬─────┘
Bank number
The following procedure will select a bank in single bank mode :
Port[EXT] := $B2;
Port[EXT + 1] := (Port[EXT + 1] And $E1) Or (bank_number shl 1);
where bank_number = 0 - 15. Each bank is 64K long and has a 64K
granularity.
Duel Bank Mode is only supported on the 18800-1 and 28800 chips. You can
map one bank to A000:0000-FFFF for read operations and another to the
same address space for write operations.
Index : B2h
┌───┬───┬───┬───┬───┬───┬───┬───┐
│ 7 │ 6 │ 5 │ 4 │ 3 │ 2 │ 1 │ 0 │
└───┴───┴───┴───┴───┴───┴───┴───┘
└───┬───┘ └───┬───┘
Read Write
Bank Bank
Number Number
The following code will set the write bank number:
Port[EXT] := $B2;
Port[EXT + 1] := (Port[EXT + 1] And $F0) Or (write_bank_number shl 1);
The following code will set the read bank number:
Port[EXT] := $B2;
Port[EXT + 1] := (Port[EXT + 1] And $0F) Or (read_bank_number shl 5);
┌───────────────────────────────┬────────────────────────────────────────────
│ ATI IsModeAvailable BIOS Call │
└───────────────────────────────┘
Int 10h
Inputs :
AH = 12h Extended VGA Control
BX = 5506h Get Mode Information
BP = FFFF Set up for Return Argument
AL = Mode Number Mode number you want to test
Returns:
BP = FFFFh Mode not supported
Anything else : mode is supported, BP = offset into CRTC table for mode