Playing with TIGA #3 – TIGA libraries and drivers

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TIGA is a strange beast. Texas Instrument’s TMS34020 (introduced in 1990) was the holy grail of 2D graphics acceleration for a certain period in the world of PCs. This chip is fully programable general purpose processor, so you can offload even non-graphics tasks to it (my low-cost SPEA Graphiti HiLite 1024 has 1MB of program/data memory in addition to 1MB of framebuffer memory). If you add a floating-point coprocessor (like Intel i860 or TMS34082), you can create a 3D accelerator that processes both rasterization and geometry processing.

On the other side, fixed-function graphics cards soon became cheaper and faster, which took the mass-market appeal away from TIGA. There were also multiple reasons, why TIGA was not a user-friendly standard. Unlike CGA, EGA and VGA, TIGA has a vendor specific part of the graphics driver. That means that you cannot just put a TIGA card in your computer and hope that programs or operating systems listing TIGA among supported graphics standards will work. That’s the reason why most TIGA collectors not even try if their cards are in a working condition.

This SPEA card (like many other TIGAs) is supported in DOS and Windows 3.x only. You need to configure the card (the configuration is stored in its EEPROM), initialize it during every boot using a vendor specific driver and load a generic TIGA library. Once all the steps are done, you can run any TIGA-enabled program.

This approach means that there cannot be any generic TIGA driver for UNIX, Linux, Windows NT and other operating systems that cannot work with drivers loaded from DOS. Windows 3.x has a generic TIGA driver and one can be installed also in Windows 95, but that’s all.

SPEA didn’t bank on the generic TIGA support in programs. They provided “direct” drivers for multiple DOS CAD programs (including AutoCAD) and Windows 3.1. These drivers work only on compatible SPEA cards and bypass all TIGA libraries. SPEA made them more performance optimized for CAD work. The Windows driver also offers an easy way to change resolution and color depth. Only 256-color (8-bit) and true color (32-bit) modes are supported, so my entry-level board with just 1MB of framebuffer memory can show millions of colors in resolutions no higher than 640×400.

(The first photo shows the SPEA card compared to a standard “dumb” ISA SVGA card. This SVGA card is one of the best choices from the early 90s thanks to its fast Tseng ET4000AX chip and 1MB of 32-bit video memory.)

SGI Indy (1993)

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This machine represented the SGI’s low-end workstation offering. It was targeted towards Mac users (DTP…) that needed more graphics and processing power than they could get from Macintosh Quadra systems. It’s a sleek pizza-box computer with just a single quiet fan inside (unlike other SGI systems). However, in comparison with non-SGI competitors, it was not slow. It had at least 100-MHz (64bit) MIPS processor, at least 16MB of RAM (reasonable configurations started with 32MB) and multiple graphics card options available. 10Mbit/s LAN, ISDN modem and video inputs (composite / S-Video / a digital port for the bundled webcam) were integrated on the logic board in all configurations as standard.

My Indy is from 1995 and has a more powerful 150MHz MIPS R5000 CPU. On the other side, it is equipped with the lowest possible graphics card (XL8/XGE8/Newport) that supports no more than 256 colors and was introduced with the early machines.

I always thought that Indy was the only SGI system without any 3D acceleration when sold with XL8 (2MB of 64bit video RAM) or XL24 (6MB of 192bit video RAM for true color modes) graphics cards. I expected just a crappy framebuffer (with BitBlt) and nothing more – like in Sun and HP machines. I was wrong. The REX3 chip inside the Newport graphics is pretty capable. Although all the 3D transformations and triangle setup are done in software, the chip can raster triangles with smooth (Gouraud) shading and per-vertex alpha-blending. Even Z-Buffering is partially accelerated using the chip (Z-Buffer is stored in system memory though).

In fact, this chip is not very far from early PC 3D accelerators (1996-1997) in terms of functions… except for the texturing support which was not available even with higher-end workstation-class 3D accelerators in 1993. This is for the first time I see 3D accelerated OpenGL (1.0) on such an old graphics card – and in 256 colors. To be correct, the scene with triangles has just 16 colors because any real-time graphics requires double-buffering. Each byte of the window in video memory contains one pixel from both buffers in the GBRG-GBRG arrangement of bits.

The graphics card is faster than I would expect. The pixel fill rate for smooth shaded triangles is ~50Mpix/s. If you add alpha-blending, you will get ~20Mpix/s. That’s 5-20 times as fast as the Windows NT 4.0 software renderer on a laptop with 133-MHz Pentium MMX and a 2D-only graphics chip. The speed in 3D is more comparable with 3Dlabs Permedia, S3 Virge DX and other consumer 3D accelerators from 1996.

A Sound Card David Made 30 Years Ago

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This is a sound card designed and built by David (a friend of mine who does most of hardware repairs here on my tumblr) in the early 90s. He was a 15-16 years old high school student when he created this thing. It’s a custom design with 12-bit DAC, DMA support and connections for mono out and mono in. He was forced to use an 8-bit ISA bus because 16-bit AT prototyping card PCBs were not available in Czechoslovakia stores at the time (not long after the Velvet Revolution). There was also a problem to get necessary parts for stereo output.

The sound card is not compatible with any standard, so he wrote a program to playback wave sounds and created a “driver” for MODPLAY to playback tracker music. His reason to make his own sound card was simple – 8-bit Sound Blasters had worse sound quality and 16-bit sound cards were too expensive for him.

He still has one of the assembled cards, a prototyping board, all technical drawings and a WordPerfect document describing the design and operation of the card.

There is a quick video of the working card: https://www.youtube.com/watch?v=rL8u9aRfaK8