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BWX does not help with unaligned accesses, but solves the fact that original Alpha did not even have instructions for memory accesses smaller than word. Which k

by dfox 2y ago

BWX does not help with unaligned accesses, but solves the fact that original Alpha did not even have instructions for memory accesses smaller than word. Which kind of becomes an issue when you start building the systems on PC-like hardware (another related “feature” is that EV5 does not have equivalent to MTRRs, but dealing with the weirdness of VGA framebuffer accesses is part of the architecture specification by means of hardcoded uncached memory region).

fredoralive 2y ago
TBH, I'm not an expert on Alpha, and wow, as an embedded programmer by trade, that's really wacky way of handling memory access. I guess it made more sense in the minicomputer world where you control the whole stack, but as a more general purpose architecture its well, not the greatest is it.
- dfox 2y ago
  There is a lot of good things to be said about Alpha and it is probably the most RISC of all 90's RISC ISAs, but the actual hardware is full of weirdness and all the real CPUs were deeply pipelined OoO designs (think Intel NetBurst) that prioritized high clock rates and huge straight-line throughput above all else (which is also why that ran really hot and could not be really scaled down for embedded use). Taking good ideas from that while discarding the “speed-demon” design is a part of why AMD become relevant again in 00's with amd64 cementing that position (but well, AMD K7 is very much Alpha-related design, to the extent that the chipsets are interchangeable between K7 and EV6. The interesting part of that is that these CPUs do not have FSB in the “bus” sense, but there is a point-to-point link between CPU and chipset).
  - fredoralive 2y ago
    AMD using an Alpha bus for early Athlons feels like a weird lost opportunity. Cheap x86 aimed motherboards that can run also run Alpha chips with Windows 2000 + FX!32 for compatibility, it might’ve had a chance to shine, albeit a slight chance. Sadly by then Compaq had already boarded the Itanic…

by dfox 2y ago

fredoralive 2y ago

TBH, I'm not an expert on Alpha, and wow, as an embedded programmer by trade, that's really wacky way of handling memory access. I guess it made more sense in the minicomputer world where you control the whole stack, but as a more general purpose architecture its well, not the greatest is it.

dfox 2y ago
There is a lot of good things to be said about Alpha and it is probably the most RISC of all 90's RISC ISAs, but the actual hardware is full of weirdness and all the real CPUs were deeply pipelined OoO designs (think Intel NetBurst) that prioritized high clock rates and huge straight-line throughput above all else (which is also why that ran really hot and could not be really scaled down for embedded use). Taking good ideas from that while discarding the “speed-demon” design is a part of why AMD become relevant again in 00's with amd64 cementing that position (but well, AMD K7 is very much Alpha-related design, to the extent that the chipsets are interchangeable between K7 and EV6. The interesting part of that is that these CPUs do not have FSB in the “bus” sense, but there is a point-to-point link between CPU and chipset).
- fredoralive 2y ago
  AMD using an Alpha bus for early Athlons feels like a weird lost opportunity. Cheap x86 aimed motherboards that can run also run Alpha chips with Windows 2000 + FX!32 for compatibility, it might’ve had a chance to shine, albeit a slight chance. Sadly by then Compaq had already boarded the Itanic…