4 ms·

Yeah it's true ARM isn't terrible the few times I've played with it. In contrast, I Verilog'd up my own homebuilt system with a RISC-V core, and didn't particu

Yeah it's true ARM isn't terrible the few times I've played with it. In contrast, I Verilog'd up my own homebuilt system with a RISC-V core, and didn't particularly reading/writing in the RISC-V instruction set.

kragen 3y ago
yeah, risc-v is nicer than 8086 or i386 or even amd64, but it's not as nice as arm. 8086 was surely 'cisc' but it's a pain in the ass
- cmrdporcupine 3y ago
  yeah my standard for "fun CISC" is the 68000, the first machine I truly wrote assembler for (after handrolling 6502 by POKEing opcodes). It was a pleasure. Though I don't miss big-endian, I can't think like that anymore.
  - kragen 3y ago
    yeah, the 68000 is fantastic! but i think the arm has all the creature comforts of the 68000 and more (though not of the 68020)
  - NikkiA 3y ago
    Makes me wonder what the m88k instruction set was like, sadly a quick search makes it look like the only programming manuals were (now expensive) physical books and there's no simple PDF online. edit: found it.. http://www.bitsavers.org/components/motorola/88000/MC88100_RISC_Microprocessor_Users_Manual_2ed_1990.pdf http://www.bitsavers.org/components/motorola/88000/MC88100_R... Looks moderately clean and easy
    - kragen 3y ago
      in terms of systems design it looks pretty decent: 32 gprs, 51 instructions, load-store architecture, 20 megahertz, one instruction per clock for alu instructions, hardware floating point coprocessor, can do fp and memory concurrent with alu instructions, hardware multiplier, delay slot bit in branches, separate instruction and data memory buses. the big thing not specified in the manual is the price; a 20-mips processor costing US$10000 in 01988 is different from a 20-mips processor costing US$10. but of course what killed it was powerpc apparently the mmu was a separate chip? with the cache on it? and that's why this manual doesn't document the page table structure? so it was only questionably a microprocessor
      - cmrdporcupine 3y ago
        of course what killed it was powerpc I thought it was already considered a failure before the arrival of the Power alliance? I seem to recall hearing about reliability etc problems with the few who tried it? I think NeXT went as far as building a box around it?
        kragen 3y ago
        the 68000 had similar problems, you couldn't reliably restart an instruction after a page fault. the sun-1 worked around this by using two 68000s. as i understand it, usually you can work around reliability problems in cmos by stricter testing (at the fab, reducing yield), lower clocks, higher voltage, better bypassing and esd protection, longer setup and hold times, bigger heatsinks, derating industrial parts to commercial grade (or military parts to industrial grade), laser trimming, or occasionally higher clocks and/or lower voltage. not always, of course parts that don't work at all are often unrecoverable, except through ridiculous workarounds like the sun-1 (one computer for the price of two!) or the 286 return to real mode via a cpu full reset (https://retrocomputing.stackexchange.com/questions/11954/how-to-switch-an-80286-from-protected-to-real-mode https://retrocomputing.stackexchange.com/questions/11954/how...) but parts that work sometimes can often be babied enough to get them to work reliably
        cmrdporcupine 3y ago
        yeah the 68k story is funny, I've heard that before, though I remembered it as Apollo that did that dual 68k trick. It always confused me why Motorola didn't just axe the original 68000 entirely when it released the 68010 (with the fix for the page fault mis-design). there was no reason to keep producing the former after the latter came out, and it couldn't have cost them any more to make the '010 and it was pin for pin compatible (I've stuffed an 010 in Atari STs here with 0 problems, for example).
        kragen 3y ago
        i think i was misremembering which company it was and you're right pin-for-pin compatible parts always have some differences: power consumption, setup and hold times, ground bounce, slew rates, noise margins, hysteresis on slow transitions, drive strength, stability in the face of capacitive output loads, endurance when subjected to overvoltage or overcurrent conditions, etc. dave jones of eevblog did a video a few years ago https://youtu.be/1VlKoR0ldIE https://youtu.be/1VlKoR0ldIE about how he shipped a bunch of defective μCurrent burden-voltage-eliminating current sensors. in his tests it worked fine, but many of his customers started reporting inaccurate readings. after sufficient debugging, he figured out that the problem happened only when its output was connected to a voltmeter with a high input capacitance, which caused its output to oscillate, introducing both noise and an offset into the readings. it turned out that one of the op-amps was going into oscillation because it couldn't handle driving that much output capacitance, a common problems with op-amps, but why was this never a problem before? he'd switched over to a second source that made a chip meeting the same specifications, but which turned out to be more vulnerable to output oscillations so, when you put a pin-compatible chip into a design in place of the original part, you have to carefully test the result to ensure that it still works properly. most times it will, but if it doesn't, you could have a product recall on your hands. worse, your customers may be incorporating your product into their own products if you pull chips without warning, for example when you start producing competitive chips, every company who designed them into a product has to suddenly switch over to their supposedly pin-compatible replacements. some of them will have their products fail unless they redesign them. they will have to pull their products from the market. everyone who designed a product incorporating your original chip gets fired, and when they finally manage to get a new job, they swear to never again use a part from your company and that's why lots of companies have been producing the μa741 and its clones like the lm741 since 01968, and why out of the 15522 different op-amps that digi-key lists as in stock, 1397 are listed as 'obsolete' and another 1042 are listed as 'last time buy'. and it's why a z80 you buy from zilog today still uses hundreds of milliamps i'm not an electrical engineer, i just play one on hn

kragen 3y ago

yeah, risc-v is nicer than 8086 or i386 or even amd64, but it's not as nice as arm. 8086 was surely 'cisc' but it's a pain in the ass

cmrdporcupine 3y ago
yeah my standard for "fun CISC" is the 68000, the first machine I truly wrote assembler for (after handrolling 6502 by POKEing opcodes). It was a pleasure. Though I don't miss big-endian, I can't think like that anymore.
- kragen 3y ago
  yeah, the 68000 is fantastic! but i think the arm has all the creature comforts of the 68000 and more (though not of the 68020)
- NikkiA 3y ago
  Makes me wonder what the m88k instruction set was like, sadly a quick search makes it look like the only programming manuals were (now expensive) physical books and there's no simple PDF online. edit: found it.. http://www.bitsavers.org/components/motorola/88000/MC88100_RISC_Microprocessor_Users_Manual_2ed_1990.pdf http://www.bitsavers.org/components/motorola/88000/MC88100_R... Looks moderately clean and easy
  - kragen 3y ago
    in terms of systems design it looks pretty decent: 32 gprs, 51 instructions, load-store architecture, 20 megahertz, one instruction per clock for alu instructions, hardware floating point coprocessor, can do fp and memory concurrent with alu instructions, hardware multiplier, delay slot bit in branches, separate instruction and data memory buses. the big thing not specified in the manual is the price; a 20-mips processor costing US$10000 in 01988 is different from a 20-mips processor costing US$10. but of course what killed it was powerpc apparently the mmu was a separate chip? with the cache on it? and that's why this manual doesn't document the page table structure? so it was only questionably a microprocessor
    - cmrdporcupine 3y ago
      of course what killed it was powerpc I thought it was already considered a failure before the arrival of the Power alliance? I seem to recall hearing about reliability etc problems with the few who tried it? I think NeXT went as far as building a box around it?
      - kragen 3y ago
        the 68000 had similar problems, you couldn't reliably restart an instruction after a page fault. the sun-1 worked around this by using two 68000s. as i understand it, usually you can work around reliability problems in cmos by stricter testing (at the fab, reducing yield), lower clocks, higher voltage, better bypassing and esd protection, longer setup and hold times, bigger heatsinks, derating industrial parts to commercial grade (or military parts to industrial grade), laser trimming, or occasionally higher clocks and/or lower voltage. not always, of course parts that don't work at all are often unrecoverable, except through ridiculous workarounds like the sun-1 (one computer for the price of two!) or the 286 return to real mode via a cpu full reset (https://retrocomputing.stackexchange.com/questions/11954/how-to-switch-an-80286-from-protected-to-real-mode https://retrocomputing.stackexchange.com/questions/11954/how...) but parts that work sometimes can often be babied enough to get them to work reliably
        cmrdporcupine 3y ago
        yeah the 68k story is funny, I've heard that before, though I remembered it as Apollo that did that dual 68k trick. It always confused me why Motorola didn't just axe the original 68000 entirely when it released the 68010 (with the fix for the page fault mis-design). there was no reason to keep producing the former after the latter came out, and it couldn't have cost them any more to make the '010 and it was pin for pin compatible (I've stuffed an 010 in Atari STs here with 0 problems, for example).
        kragen 3y ago
        i think i was misremembering which company it was and you're right pin-for-pin compatible parts always have some differences: power consumption, setup and hold times, ground bounce, slew rates, noise margins, hysteresis on slow transitions, drive strength, stability in the face of capacitive output loads, endurance when subjected to overvoltage or overcurrent conditions, etc. dave jones of eevblog did a video a few years ago https://youtu.be/1VlKoR0ldIE https://youtu.be/1VlKoR0ldIE about how he shipped a bunch of defective μCurrent burden-voltage-eliminating current sensors. in his tests it worked fine, but many of his customers started reporting inaccurate readings. after sufficient debugging, he figured out that the problem happened only when its output was connected to a voltmeter with a high input capacitance, which caused its output to oscillate, introducing both noise and an offset into the readings. it turned out that one of the op-amps was going into oscillation because it couldn't handle driving that much output capacitance, a common problems with op-amps, but why was this never a problem before? he'd switched over to a second source that made a chip meeting the same specifications, but which turned out to be more vulnerable to output oscillations so, when you put a pin-compatible chip into a design in place of the original part, you have to carefully test the result to ensure that it still works properly. most times it will, but if it doesn't, you could have a product recall on your hands. worse, your customers may be incorporating your product into their own products if you pull chips without warning, for example when you start producing competitive chips, every company who designed them into a product has to suddenly switch over to their supposedly pin-compatible replacements. some of them will have their products fail unless they redesign them. they will have to pull their products from the market. everyone who designed a product incorporating your original chip gets fired, and when they finally manage to get a new job, they swear to never again use a part from your company and that's why lots of companies have been producing the μa741 and its clones like the lm741 since 01968, and why out of the 15522 different op-amps that digi-key lists as in stock, 1397 are listed as 'obsolete' and another 1042 are listed as 'last time buy'. and it's why a z80 you buy from zilog today still uses hundreds of milliamps i'm not an electrical engineer, i just play one on hn