The HISPEC Project Official Enthusiasts' Guide Alpha Version - Last updated 8/10/98
(Mostly) written and (entirely) edited by Rob Alexander Comments in [] are by me. Numbers in [] are references to the footnotes at the end of this file. Not everything in this file is written by me, but I've chopped and changed so much that it would be hard to pick out specific bits that were one other peoples'. So if you think you should be on the 'also starring' list, or claim that something hear is yours and you want it back, e-mail me. (u8k62 [at] ugk.keele.ac.uk).
Thanks to: Andrew Toone, Luis Commins
Introduction - Project Overview The HISPEC Project is a internet-based project to create a new computer system, using the Sinclair ZX Spectrum as a conceptual guide. The proposed system has been compared to "A Spectrum for the 90s". The blueprints will be protected by something comparable to the GPL: a copyleft licence that allows anyone to access and distribute the plans (even for money) but [******what!*****help!****]. In this respect, Linux is our conceptual model. There are great difficulties inherent in transferring this concept to hardware, but together we will overcome them, and thereby rule the world! Mwa-ha-ha-ha-ha!!!!!!!!!! [1]
Current thinking is that computer hobbyists who want a HISPEC will buy the various parts and put them together. For some components (the main PCB and possibly the CPU) these will have to be manufactured and/or attached by a professional using specialist equipment, probably in bulk if it is to be affordable. This poses organisational diffuclties. In any case, it seems desirable for someone to set themselves up as a manufacture and distribution bloke [better word?]. They could then provide ready-made HISPECs to those who don't have the skills to make their own. Under the GPL-like licence it would be perfectly permissible to charge for the construction time.
Project Status
The project is in the very early design stages. At present, the mission statement is being debated, and the CPU is being researched. There has been some discussion on the topic of the GUI for the OS.
Mission Statement
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Version 1: 2/9/98
The aim of the project is to create the a complete (i.e. ready to build from) design for a home computer in the manner of the original ZX Spectrum.
It must:
a) Be cheap to build (in the region of £100/$160).
b) Provide Pentium-class performance.
c) Be simple enough to be assembled by a skilled computer hobbyist using nothing more advanced than a soldering iron.
d) Be generally easy for a beginner to program, and include a suitable (BASIC-like) programming language in ROM that provides access to all the machine's capabilities.
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HISPEC vs. SpecBoy
The HISPEC project grew from what looked like another round of the interminable 'Spectrum for the 90s' topic on comp.sys.sinclair. This time round (and last time round...) various people suggested making some kind of portable Spectrum. From the combination of this with the 'Mad Plans...' post grey the SpecBoy.
The SpecBoy was envisaged as purely a portable Spectrum. General feeling is that it would have various extra bits (e.g. ROM cartridge slot, maybe even a hard drive to store games on) but would otherwise work as a Spectrum, spec and all. In other words, the key difference between the HISPEC and the SpecBoy is not portability but the power of the system core. There has often been confusion whether 'the project' or any such nebulous term applies to the desktop HISPEC or to the SpecBoy.
It now seems that the two projects are technically seperate, but will develop together for the moment and share ideas and skills. For the moment, they are also sharing a web page. Myself, I like the (pipe dream, no doubt) of a HISPEC that's fully portable (integral screen and maybe keyboard) but is also fully functional as a desktop machine (TV/monitor link, mains supply, external PC keyboard). Component Specifications CPU The CPU is the heart of any conventional computer system. For a very basic system like the HISPEC, its importance is even greater. There are several possible candidates, all outlined here. The costs are for single chips, generally costs are less when bought in bulk.
The CPU for the HISPEC really needs to be readily available and likely to remain so. This may rule out (although unfortunately its hard to tell in advance) many of the more unusual CPU designs. The key features of the HISPEC CPU are the ability to run programs from external RAM and provide general purpose I/O. This rules out several DSPs, which would otherwise have great potential. Because of the low-complexity requirement, the chip should produce ram interfacing signals on its own, without support chip. Most modern, conventional CPUs (e.g. the Pentium) are ruled out by this. The type of package that the actual chip is supplied in is an issue. PQFP packaging is suitable for hobbyist work, BGA is not. It has been suggested that we could get around this by putting the CPU on a daughterboard, and having the chips attached to it commercially.
The Chips
Z80 & Z380:
Z80 @ 3.5MHz
Z380 @ 18MHz ~£10
Z380 @ 25MHz 12 MIPS
The Spectrum used a 3.5MHz Z80 as its CPU, so it was suggested that its spiritual successor should use it too. Opinion was heavily against this idea, at least in a single-CPU situation, as neither the basic Z80 or its newer, 32 bit, brother the Z380 provided anything like the performance we wanted.
ARM7500 & ARM7500FE:
ARM7500 @ 33MHz 30 MIPS
ARM7500FE @ 40MHz 36 MIPS
ARM7500FE @ 48MHz: I am informed that it can be clocked at this speed so I have extrapolated from the 40MHz figures. The spec for this chip can be found (somewhere) at www.arm.com. In summary: it's a glueless chip with onboard video, sound and IO controllers. ARM describe it as "a single-chip computer" and, while this is perhaps a slight exaggeration, using the ARM7500 looks to be a very easy option from a design perspective. For a while the ARM looked like the ideal CPU for the HISPEC.
As well as being available at higher clock speeds, the FE is equipped with a limited form of floatng-point acceleration. I believe that using this may require special programming, either in apps that use it or in the OS itself. Unfortunately the performance of the ARM is still rather lacklustre, being considerably less than Pentium-class (more like a fast 486). With the discovery of the NEC VR4101, it looks unlikely that the ARM be our choice of chip. Although ARM make many faster chips, none of them have the integrated systems that the 7500 has. Casio make/use a variant of the 7500 that is marginally faster than the FE, but not enough to make a real difference.
PowerPC 403GCX & 750:
403GCX @ 80MHz 99 MIPS $43
750 @ 266MHz 550 MIPS $288
The 403GCX was the original suggestion for the HISPEC. It is largely glueless, incorporating a variety of bank controllers . It is designed for embedded use, and is therefore has relatively simple 160-pin PQFP packaging. The 750 was perhaps something of a dream, as it provided awesome power. Unfortunately its a state of the art desktop computer CPU, with a price tag to match. It is only available in BGA format, which is nearly impossible to work with in a hobbyist situation.
NEC VRxxxx series:
VR4101 @ 33MHz 80 MIPS £16.50
VR4111 @ 100MHz 130 MIPS £35
VR4310 @ 167MHz 221 MIPS
VR5432 @ 250MHz 519 MIPS
There are datasheets for these 64-bit chips on the NEC site (www.nec.com) in .pdf format. The unit apparently has much of what the ARM does (LCD, keyboard, IrDA, Serial, DAC/ADC), but unlike the ARM it would still need some support chips. Additional support chips are available which handle colour LCDs, PCMCIA, etc. The NEC4101 is supplied in 160-pin LQFP format. See PQFP in the glossary - it's definately a plastic package, the 'L' may stand for low-profile. Reading the NEC materials suggests that this chip is limited to using a maximum of 8MB DRAM, which is really too little.
The 4111 is only supplied in 224-pin FPBGA packaging. This is potentially a problem, but there may be ways around it. It supports up to 64MB of DRAM. A new chip, the 4211, is rumoured to be on its way. It's essentially an update of the 4111, rated at 230 MIPS. There are more advanced chips in the range, such as the 4310 and the 5432.
Unfortunately, neither have the 'computer-on-a-chip' functionality of the 4101, and both require hefty glue logic because of their multiplexed address buses. Both are rather greedy in terms of power, pretty much ruling them out for the SpecBoy. The package for the the 4310 (120 pin QFP) is reasonable, while the 272 pin ABGA of the 5432 is not.
StrongARM Series:
MIPS: Cost: SA1100 @ 220MHz 250 MIPS
These RISC cpus are based were developed by ARM, but they are manufactured [solely?] by Intel. They are used by Acorn's range of RiscPCs. They are noted for their relatively low power consumption and heat output. (For example, the 220MHz version dissipates less than 550mW). The SA1100 is a fairly conventional design, but does have LCD control circuitry built in. A 'companion' chip is available (the SA1101) which provides support for keyboard/mouse, USB, video (i.e. monitor rather than LCD) etc. The SA1100 is available in 208pin LQFP and 256pin mBGA packages.
The Multiprocessor Issue
The idea of allowing the HISPEC to be equipped with a variable number of processors has been raised. It has also been suggested that it should be possible to link up several distinct HISPEC systems to pool their resources. Implementing such a system will raise the complexity of the hardware and operating system software required. Because of unavoidable overheads in a parallel processing situation, combining two processors will not double the overall power, and this will be even less true for combing two seperate systems. Display It has been suggested that the HISPEC should use: an integral LCD, a external LCD, a TV connection.
The integral LCD was more of a SpecBoy idea, but the external LCD has been suggested as a HISPEC add-on. A significant disadvantage of using a colour rather than mono LCD in a portable machine is the massively higher power used. Compare the Sega Game Gear (typical battery duration 55 minutes) with the Nintendo Game Boy (typical battery duration 20 hours).
I/O: The current plan is for the HISPEC to have a couple of USB ports and a general expansion slot with full processor/system bus access. The USB ports will give it access to hard drives, joysticks, 'web cams', floppy drives, etc. The expansion port is geared towards the hobbyist but hopefully some additional processor modules will be made to slot in here. Networks & Other Links Following on from the system combining idea, it has also been suggested that networking should be a key part of the HISPEC. Since they should be, relatively, very cheap to obtain, it wouldn't be too unusual for two or more HISPECs to be available for connection.
Glossary Footnotes [1] As a point of interest, the original spec for the system was proposed by Andrew Toone on the newsgroup comp.sys.sinclair under the subject 'Mad Plans for World Domination'.
