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/  Forum Index
   /  Amiga OS4.x \ Workbench 4.x
      /  A-EON is internally testing Alpha releases of their own operating system
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PosterThread
Hypex 
Re: A-EON is internally testing Alpha releases of their own operating system
Posted on 11-Aug-2021 7:14:35
#141 ]
Elite Member
Joined: 6-May-2007
Posts: 11180
From: Greensborough, Australia

@matthey

Quote:
That little trapCode() function would use the following stats then. PPC: 23 instructions, 92 bytes 68k: 12 instructions, 32 bytes The 68k uses less than half the instructions and has nearly 1/3 of the code size while the code is much easier to read. Why did Motorola think PPC could replace the 68k for embedded markets again?


They must have got sucked into the AIM alliance. And then tried to make up for it with the ColdFire 68K abomination, another CPU that misses out on 68K features. What they should have done, is what they were doing, jump on the RISC bandwagon with the 88K follow up instead of abandoning it. Well, perhaps.

Quote:
I always wondered why all programs didn't get a pointer to ExecBase passed in at startup like interrupt handlers. The code isn't any longer on the 68k for using absolute short addressing to access address $4 and in the beginning was no slower as any access was from chip memory. When fast memory was added to Amigas, it was faster to access a cached value in fast memory rather than in chip memory. The zero page was later remapped to fast memory with the MMU on some Amigas so both accesses are equally fast again but it is still faster for all Amigas to cache the address in fast memory.


Standardising this in the ABI would have helped. A0 and D0 were used for args and argl. This is analogous to to argv and argc, meaning arg string and arg length in my case. So pre-loading ExecBase to A6 made sense.

Quote:
move.l lr,r8

Here is 68k format now. If I had my way, I would make the 'e' in "move" optional on the 68k though.


Actually, it depends on the assembler format, I discovered 68K can be written as "mov" along with different conventions for things like indirect addressing.

But, unlike 68K, the order on PPC is backwards. With destination before source. The operands are in backwards x86 order.

Quote:
x86 needed more optimization or at least it had more opportunities for optimization. Yes, the best compiler technology did evolve from supporting the x86 architecture and all other architectures were at a disadvantage. PPC received pretty good compiler support at one time but I expect support is already starting to diminish. Like the 68k, compiler support is unlikely to disappear altogether but often so called newer compiler technology has not been able to surpass GCC 2.95.3 code generation which was just starting to get good. Newer compilers do more work often to produce inferior code.


That tends to be the the bench mark. Been a long time since. But like AHIv4 nothing since appears to have matched it.

Quote:
If all Trevor wants is the fastest Amiga play toy he can buy, then indeed a POWER Amiga would give it to him while wasting a lot of parallel processing potential and having no future as POWER went even bigger and more expensive in the latest generation. The A1222 was clearly aimed at the lower end of the Amiga market to boost users and development but it looks like the price and compatibility will fall short of the goal if it ever comes out. He is making the same mistake as Motorola did trying to replace the 68k with PPC in the low end embedded market. It is pretty clear what Amiga customers want for the low end which is the 68k and Amiga chipset compatibility. Low end PPC hardware has been disappointing customers for decades.


The POWER machine should have more future than the current pick of the crop, since unlike the current crop, you can still buy it and have it configured like a desktop. But wasted power is a result of a means to an end. The end is to bring a decent OS4 machine to the users with high price and POWER is the best I've seen that is able to do it. Besides, it can still run Linux fully, and likely one already able to boot it unlike the custom kernels needed now without a full installer. Wasted power becomes a side effect. Right now, POWER9 users are out there, criticising the X5000 as a joke. When POWER users are hanging crap on other PowerPC people, in an x86 world, you know it's bad.

What stalled the A1222 was the esoteric CPU chosen. If I was at the planning meeting that day I would have said no to a rare PPC chip rarer than PPC itself. One that is now extinct in PPC land.

But, low end Amiga customers have no interest in PPC and OS4. In fact MOS can be run on cheaper hardware. Or a more expensive X5000. The A1222 did get interest from it's lower pricing point, even from the 68K crowd. And the A1222 would easily be faster than the fastest 68K Amiga.

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Hypex 
Re: A-EON is internally testing Alpha releases of their own operating system
Posted on 12-Aug-2021 13:16:08
#142 ]
Elite Member
Joined: 6-May-2007
Posts: 11180
From: Greensborough, Australia

@IridiumFX

Quote:
I apologise, I am not really into AOS 4 ABI, but rather than "virtual 68K registers", or the double indirection of a struct->funtion(struct, args), what's preventing a base + displacement call on the PowerPC, like the exec of old ? Are you aware of any specific reason ?


In simple terms, the PPC doesn't have any kind of JSR call that can do the base + displacement. Like most operations on PPC, it must be done manually, with a few instructions in line. In this case loading the function pointer into a register, then moving it to a callable register and finally calling it from the register. So neither calling from a base offset nor loading an address into the function register is possible.

However, branches can be done directly, as per normal. Likely that branching would be used internally in the OS like it did on 68K. Libraries are small enough and even the whole Kickstart code could be cross branched if it was in one block of memory.

And in the "struct->funtion(struct, args)" case, that's what 68K had to do as well, since the base had to be loaded into the base register and called off it.

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