PERIHELION'S PARALLEL UNIVERSE Much excitement was generated when Atari announced its plans toback Perihelion in the development of a transputer-based work-station, known to all until recently as the Abaq - now called'The Atari Transputer Workstation'. As the project is now nearingits finish, David Gristwood met up with some key members of thePerihelion Team. Perihelion was formed by Jack Lang and Hugo Davenport. The wordPerihelion is derived from the name given to the earth's closesttransit to the sun. The literal translation 'the closest pointto the sun' is indeed apt, for one of Perihelion's biggest ri-vals will be computer company, Sun! Perihelion's original inten-tion was to produce a low-cost, high-performance workstationwith very high resolution graphics. Their attempts to get ven-ture capital to design, build and market it in the UK failed. Eventually they approached Atari, who, it turned out, had beenthinking along the same lines. Atari bought the rights to themachine, leaving the design of the hardware to Perihelion. Atarihas not, however, taken up the rights to software, and it ishoped that the operating system developed by Perihelion will be-come the standard for transputer-based computers. Perihelion is actually two separate companies: Perihelion Hard-ware and Perihelion Software (the hardware division is alreadywell known in connection with the Laptop ST currently under de-velopment for Atari). Perihelion Hardware, based in Cambridgeand headed by Jack Lang, designed the Abaq / Atari TransputerWorkstation. The operating system for the machine was developedby Perihelion Software, under Time King at Shepton Mallet inSomerset. The Atari Transputer Workstation is targeted at a number ofareas that require good graphics and high computational through-put. Typically, these include desktop publishing, 3D solid mo-delling and various computer simulations. However, animation isan area where the ATW should excel, as it will be possible toplug the machine into a video recorder. A less obvious role isin speech recognition, at this needs the massive computationalpower that a network of transputers can supply. The ATW may alsofare well in the more conventional jobs, such as, spreadsheets,databases and word processing, where the extra power that themachine offers can be used to improve the user interface, suchas windowing and graphics. For those who have the money tospent, it would, without doubt, make the ultimate game machine!The Atari Transputer Workstation should compete well with pro-ducts such as the Max II and the Sun workstation. What the ATWreally needs is a couple of software packages that quite simplywould not be possible on any other machine, in much the same waythat VisiCalc made the Apple II and Macpaint made the Macintosh. HARDWARE The design work for the Atari Transputer Workstation has beenrunning to a very tight schedule. The specification for themachine was ready at the start of July '87 and just four monthslater Perihelion had produced five prototype macines for dis-play at computing show, Comdex, in Las Vegas. What many at theshow did not know, was that some of the final chips had not ar-rived until the last day of October. With Comdex due to start onthe second of November there had been no time to fix them intothe machine, so the Perihelion team had had to fly out to LasVegas and solder the chips to the board in the hotel room. For-tunately, the chips worked the first time. At the heart of the Abaq / Atari Transputer Workstation is aT800 transputer (for more details about the transputer see issue29 of ST World). This is a 20MHz model with an on-board float-ing point unit, capable of 1.5 mega FLOPS (million FloatingPoint Operations Per Second). In addition there is a gate arraychip, named Charity, that performs a whole host of functions,including blitting. The basic configuration for the Atari Trans-puter Workstation is 4 Mbytes of RAM, though there are fourinternal expansion slots. The ATW is equipped with a configura-ble block that allows access to the transputer links in theirnative form, directly from the transputer, or TTL (Transistor-Transistor Logic) buffered, or ECL (Emitter Coupled Logic),buffered which provides much better signal integrity over longdistances. It is estimated that at 20 MHz using the ECL buffersit should be possible to drive at least a 100 feet of cableusing standard RS423 cabling, thus eliminating the need forexpensive coax cables. The four slots on the expansion bus have been designed to workwith either memory or transputer farm cards. Each farm card(farm is the collective noun for transputers) has four T800transputers, each with its own 1 Mbyte of memory, arranged asa square. The spare transputer links, eight in all, are broughtout to connectors on the edge of the board. The memory cards forthe expansion slots each hold 20 Mbytes of RAM, giving the AtariTransputer Workstation a maximum expansion potential of 64 MB. On the developer's version of the machine there is a link to anAtari Mega ST, though om the production version there will be acut-down Mega ST on a board inside the machine itself. The MegaST is used as the I/O (Input/Output) processor. TraditionallyI/O is the bottleneck in the sytem, so assigning a separateprocessor to the task will free up the Transputer for othertasks. Special logic is required to allow the 68000 to communi-cate with the transputer, but it enables the ST to take care ofall the I/O processing. The Atari Transputer Workstation iscapable of very impressive high resolution graphics and thereare, in total, four different display modes. Mode 0, has a reso-lution of 1280 by 960 pixels, with four bits per pixel. Thisallows sixteen colours on the screen simultaneously from a pa-lette of 4096, though this mode may also be used for a mono-chrome display. In both modes 1 and 2 there are eight bits perpixel. Mode 1 has a resolution of 1024 by 768 and through alook-up table there can be 256 colours on the screen from apalette of sixteen million. Mode 2 has a resolution of 640 by480 and is multi-buffered, which should allow for animation. Mode 3 is 512 by 480 pixels, where each pixel is 32 bits. Thisis divided up into eight bits per colour, with the spare bitsholding overlay and tag information, giving a possible sizteenmillion colours or so (more than can be displayed at the screenat one time!). The frame rates for all the displays are 60 or70 Hz, which reduces the screen flicker to an absolute minimum. The pixel clock rates vary from 25 MHz for the lowest resolutionmode up to 102 MHz for the highest resolution mode. The designof the video sub-system is modular, so there nothing to preventthe machine being driven in alternative video modes using add-onboards with different crystals. The Atari Transputer Workstation requires 1 Mbyte of video RAMto support these graphic modes. It is important that this videoRAM is dual ported, for otherwise, reading out the video to putin on the screen would take up some of the bus band-width,effectively slowing the processor down. As it is, the video sidetakes only one or two percent of the total bus band-width. Thespectacular graphics are made possible by a gate array chip cal-led Charity. This was designed by Richard Miller, who also desig-ned the gate array for the Sinclair Z88 portable computer. Chari-ty has two main functions. The first of these is to 'mop up' allthe logic on the board and this includes memory control and re-fresh, bus arbitration and controlling video scanning and syn-chronisation signals. Its other role is as a blitter, performinghigh speed graphics manipulation. Gate array chips consist of alarge number of gates (each of which is made up of four tran-sistors) that are connected together indifferent combinations inorder to supply the logic for a system. Charity is designed onto an 8500 element gate array and it uses97 percent of the gates available on that array (this is a veryhigh ultilisation indeed, as it is not uncommon to find 20 per-cent of the gates on a gate array chip remain unused). The blit-ter on Charity occupies about half the array. Extensive use ofCAD (Computer Aided Design) workstations and computer simulationswas necessary to achieve this high usage on what is a very com-plex chip. The blitter can write simultaneously to all 32 RAMs inthe video array, enabling it to achieve very high speed perfor-mance. It is able to do this because of the clever way it handlesadress decoding. Instead of writing one word at a time, it isable to write four words simultaneously by selecting the requiredchips. Different patterns are created by masking out differentchips. The gate array that will appear in the production model ofthe ATW will be a Charity 2, to be known as 'blossom' in thefinal version. It is still being designed and will perform evenfaster as well as support a host of new features,such as, hard-ware line drawing. The Atari Transputer Workstation has been specially designed toallow fast pixel manipulation. On the Atari ST, performing x,yaddressing of pixels is a relatively complex operation becausethe pixels are packed into 16 bit words. Time-consuming and comp-lex masking operations are needed to set or clear particular pix-els. As the transputer is not suited to shifting and masking, theATW supports three different video maps, which are ways of look-ingat the video RAM. Although the ATW doesn't actually have amode that is one bit per pixel, in its highest resolution, mode0, there are four bits per pixel. One of the video maps lets theprocessor perform byte addressing to access single pixels. Thisallows fast pixel access, for given the x,y address of the pixel,it takes just a simple shift operation to come up with its me-mory address. Similarly, there is another video map which is op-timised for modes 1 and 2 and another for mode 3. Suitable monitors: - NEC Multisync Plus/XL........Modes 1,2,3 - Hitachi 4615-D-BB-3...............Mode 0 - Philips M1964.....................Mode 0 The ATW will support the following screen resolutions: Mode Resolution Bits/pixel Colours Palette 0 1280*960 4 16 4096 1 1024*758 8 256 16 million 2 640*480 8 256 16 million 3 512*480 32 True colour, every pixel a different colour SOFTWARE A workstation such as the ATW requires quite a sophisticatedoperating system to interact fast and efficiently with the hard-ware. The problem is that at present there is no standard operat-ing system which will run on the transputer. The transputer wasdesigned to be part of a multiple processor system. It has itsown special hardware links which allow high-speed communicationsbetween processors and its instruction set supports process crea-tion, switching and time slicing. Perihelion's solution to thisproblem was to create Helios, a new operation system that wouldbe 'sympathetic to transputer architecture', exploiting itsstrengths as well as concealing some of its weaknesses. Helios isnot tied to the ATW, but is intended to run on a wide range oftransputer system configurations. Nick Garnett (who. like TimKing, is ex-Metacomco) did much of the design work before Peri-helion was formed and is in charge of the development at Perihe-lion. NBy June '88 most of the work on Helios was complete andTim King gave a demostration of a working version of the systemto delegates at Miroway's Transputer conference at the PC Usershow. The only part of the system that is still to be finished isthe windowing interface and this is due for completion soon. Helios is what is known as a 'distributed operating system'. Theresources for the system, such as memory, backing store, printersand even processors themselves, can exist in different locations. The sharing of these resources is transparent, relieving the userof the burden of having to know the exact details of the system. This setup differs from the more conventional multi-user systemin which the terminals and other resources are connected to onecentral processors that shares its time between each of them. Italso differs from a standard network, where each workstation hasits own processor, but the processors cannot be shared and thereis limited sharing of other resources om a local basis. A distributed system has a greater degree of reliability thanconventional systems, for if a processor fails, the rest of thesystem can still carry on, though this may be at a reduced capa-city. One of the biggest attractions of a distributed system,though, is its ability to harness unused processors in the sys-tem. A program could call upon spare processing power from aworkstation that is not in use, or a workstation which hasmultiple processors, not all of which are being used. With seve-ral transputers working together, one workstation could outper-form a conventional minicomputer. Each workstation in a Helios network must contain at least onetransputer. Each transputer must run the Nucleus, a programwhich controls the resources connected to it, so that they canbe intergrated into the network. Helios is based on a client-server model, where each user runs a number of tasks that re-quest services from system-provided server tasks. These servertasks can be running anywhere on the network, but their locationdoes not to be known by the requesting program because the mes-saging-passing system ensures that each message reaches its des-tination, whereever that may be. A mechanism known as 'capabilities' is used by Helios to protectobjects. Encrypted access rights are used to determine whether aprogram's request to access a particular object should be grant-ed or not. This technique means that it is possible for no oneuser to have full access rights to everything, which, in turn,means a more secure system. There are three strategies available for running programs underHelios. The first of these makes no use of the distributed na-ture of the system and runs a task as a single process on asingle transputer. This method allows programs to be taken froman alien environment and to be run by recompiling and linkingunder Helios. The second method is to break down a program intoseveral discrete parts. These can then be as separate tasks,each occupying a separate processor if available. These tasksthen communicate with each other via a message-passing systemknown as a pipe. The final method is to write programs thatmake explicit use of parallel algorithms. Although this is themost complex option, it can extract the maximum performancefrom the processors. Interaction with Helios is by way of two interfaces. The firstof these is a CLI (Command Line Interface) that closely resem-bles the Unix C-Shell and the standard Uniex utilities. Forthose who feels more comfortable with WIMPs (Window-Icon-Mouse-Popdowns), windowing and mouse support will be available throughthe public domain X-Windows V11 interface. Surprisingly, Helios was not written in Occam, the language ofthe transputer (for more details about Occam see issue 28 of STWorld) but in a mixture of C and transputer assembly language. The kernal was written in assembler to keep it small and effi-cient, whilst the rest of the system was implemented in C, alanguage which is well suited to writting operating systems andis renowned for its portability. Occam is supported by Heliosthough and a number of third part developers are already workingon a variety of compilers, including Pascal, Fortran, Lisp anBCLP. A TECHNICAL LOOK AT THE ATARI TRANSPUTER WORKSTATION The Atari Transputer Workstation, formerly known as the Abaq, un-til it became clear that a company in Europe had rights to theproduct name Abaq (from the root of the Greek word for 'sand', asin silicon - the primary constituent of intergrated circuits -and also linking with the word 'abacus'), is a very powerfulworkstation-type, stand-alone computer based upon the InmosT800-20 transputer. The architecture consist of a motherboard, abackplane card and up to four expansion cards which will typi-cally be additional 'farmcards' each containing 4 transputerswith up to 16MB DRAM per transputer. A fully populated farmcardconsumes about 12 Watts of power. The Atari Transputer Workstation's motherboard consists of 4MB offast DRAM (120ns) expandable to 16MB (eventually 64MB), one T800transputer, a 68000 processor with with 512K RAM to hande all theI/O, 1MB of fast dual-ported video DRAM (100ns) connected to bothmain bus and video bus. The gate array chip 'Blossom' will handleblitting and also perform most of the 'gophering' tasks that alot of the chips in today's computers find themselves doing. TheI/O capabilities parallel the facilities found on a conventionalMega ST, in essence: RS232c, DMA (ACSI), parallel, MIDI,720K 3.5" floppy, with the addition of full SCSI. Both the maintransputer system and the 68000 I/O subsystem can be expanded -the 68000 bus is available via 1 expansion slot, the T800 bus isavailable via 3 expansion slots. Into the motherboard plugs a backplane card, which provides fourbus sockets. Into these can fit the farmcards. These farmcardsare the same as those used in the Polyhedron unit memtioned inthis month's news pages. These do the same as the single trans-puter system on the motherboard, but provide an expanded powercomputing environment, with a fully expanded ATW providing upto 13 transputer systems internally for distributed processingenvironments. By using auto-linking cross-bar switching boardsbased on the Inmos IMS C004 programmable link switch, an entiresystem can be reconfigured dynamically as if the machine's ar-chitecture were being hard-wire redesigned in mid-program. Thepre-production units seen at this year's PC show were in AtariPC3 cases - the final production models will most likely livein upright AT tower-type cases which stand on the floor. Allthis and more for less than œ5000.