On Wed, 23 Apr 2008, Dmitri Vorobiev wrote: > After I had saved a DECstation 5000/200 from a junkyard a few years > ago (very neat hardware, actually), I did some research on this brand. > AFAICT, all MIPS-based DECstation models were UP. As were all the TURBOchannel Alpha machines which may eventually reuse many bits of code. That does not mean code should not be written in a clean and portable way and all the associated atomic operations and spinlock types will be optimised away when built for UP. BTW, DEC actually used to manufacture a MIPS-based line of SMP computers. It was called DECsystem 5800 and supported up to four CPU boards. Similarly to the DECsystem 5400 and 5500 computers the design was based around an existing VAX cabinet with the CPU cards using MIPS R3000 processors rather than VAX ones. As a curiosity the systems included a low-end VAX processor as well, as a service unit for the purpose of console diagnostics and system bootstrap. The main CPU would be kept frozen until an OS was loaded at which point the MIPS unit would get unlocked and start executing while the service procesor would get halted. AFAIK, the operation was controlled by some external register and was atomic, never allowing the two processors to run simultaneously. Conceptually it was similar to how the original VAX-11/780 and its console operated. We will probably never support any of these systems as getting these pieces of hardware is problematic and then you need to use a lorry to move them around. Support for SMP operation of the 5800 would be particularly tricky, because, as we all know too well, ;) the R3000 did not support atomic operations and bus lock logic for atomic RMW cycles was provided by the chipset. All the relevant bits of code would have to be modified to make use of it. I am told NetBSD folks have had some success with one of the machines; the 5500, I think. These DECsystem computers were designed by a different group to one which did all the DECstations (WSE). The same group also designed a small box called DECsystem 5100 which was also similar to a VAX computer. We have some initial support for this machine implemented and if I got my hands on an actual piece of hardware, I might consider getting it into a better state. Chances are our code as it is would crash on this system immediately ;) -- otherwise the only supported peripheral might be the serial port. Maciej
