[Simh] BLISS ( was Re: 101 Basic Games for RSTS/E (was Re: PDP11 on Simh for public access))

[Paul Koning]

> On Jan 26, 2018, at 4:59 PM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> On 2018-01-26 22:49, Timothe Litt wrote:
>> ...
>> There also was the argument that you really couldn't (well, shouldn't) write pure assembler for Alpha because the best scheduling depends on the implementation (how many execution units, of what sorts & latencies; predictions, speculations, prefetch; etc.)
>> PALcode has some unique constraints that do require manual scheduling, as do some diagnostics.  But it does turn out to be true that Alpha assembler is best understood (and used) as a low-level compiled language, not an assembler.
> 
> Are we talking about MACRO-32 or Alpha assembler now? They are two different things. PALcode, I would assume, you actually wanted an Alpha assembler for. Porting lots of VMS stuff needed the MACRO-32 compiler. Exactly what Paul was doing, and in which language, was a bit unclear to me. I was assuming he was talking about Alpha assembler, and not MACRO-32, but I could be wrong.

Yes, native Alpha assembler.  Obviously that is machine dependent if you're optimizing very seriously.  The purpose of the exercise was to see if you could do TCP checksum in software while moving network data between the Ethernet NIC buffers and other places, at the same speed as a simple memcpy.  The answer is yes: if you're at all careful, you can do the necessary arithmetic at times when the CPU would otherwise have been waiting for memory accesses.  The same tends to be true for simple data processing actions on buffers in many other machines, for that matter.  Many years later I did RAID-5 and RAID-6 (XOR based) in software in a similar way, the cost was simply that of passing over the memory buffers and the arithmetic involved had an effective cost of zero.

	paul