80286 ATX mainboard based on the IBM 5170 AT PC

Re:80286 ATX mainboard based on the IBM 5170 AT PC by toast0 on Wednesday November 13, 2024 @02:58AM (#42123818)

IRQ jumpers weren't too bad, but it was easy to run out of them, and not all devices could share interrupts well. PCI made IRQ sharing more accessible, but the real improvement was (in band) Message Signalled Interrupts, which allows for a much larger number of interrupts, ending sharing in most cases and also resulting in a knowable ordering between I/O and interrupts, which can eliminate the race condition between interrupt arrival and status reads/interrupt enable.

The other big pains of ISA were finding working I/O assignments with lots of cards, and finding DMA channels (although ISA devices started doing their own bus mastering DMA because the motherboard DMA controllers were a fixed, slow, speed, by spec)

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by einr on Wednesday November 13, 2024 @03:04AM (#42123843)

IRQ sharing on PCI came with its own pains though which were sometimes harder to diagnose and fix. In the early 2000's I was recording and mixing music with DAWs on Windows 2000 and you always had to be very careful that your PCI ASIO sound card did not share resources with anything else or you got to deal with dropouts and glitches. Plenty of futzing around in BIOS setup and Device Manager, very flaky stuff.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by toast0 on Wednesday November 13, 2024 @03:25AM (#42123961)

Definitely. Sharing was better than not being able to use your slots when you ran out of IRQs, but sharing wasn't great. The idea of wiring 4 IRQs to the slot and let the card/driver pick was good, but the reality wasn't great if your motherboard just tied all 4 to the same pin on the interrupt controller.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by rkagerer on Wednesday November 13, 2024 @07:05AM (#42125315)

but it was easy to run out of them

So often in computing we've completely overhauled the stack with loads of new complexity, when simply adding more of some limited but unexpectedly popular resource would have sufficed (great example... IPv6).

(Ps. Thanks for your informative reply to my comment)

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by thrw42A8N on Wednesday November 13, 2024 @08:19AM (#42125822)

How do you propose we add more IPv4? Not to mention that the IPv6 protocols are less complex than IPv4 - as they were designed after the "natural" evolution of IPv4 concluded.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by actionfromafar on Wednesday November 13, 2024 @08:58AM (#42126138)

One could have made an overlay network on top of IPv4, where applications (and/or operating networking stacks) could have been aware of how to manipulate the data. Majorly more kludgy, but feasible. A number of real IPv4 addresses would have been allocated to serve as gateways/proxies to access the new IPv666 network.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by aidenn0 on Wednesday November 13, 2024 @02:25PM (#42129054)

That sounds a lot like TRT; NAT64 seems to have been more successful. See https://en.wikipedia.org/wiki/IPv6_transition_mechanism for all of the various flavors of mixing ipv6 and ipv4.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by kbolino on Wednesday November 13, 2024 @08:46AM (#42126040)

Add a little more to this number here, and a little more to that number there, piecemeal and conservatively, and before too long you have more complexity than if you just designed for larger numbers in the first place.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by cduzz on Wednesday November 13, 2024 @08:58AM (#42126139)

Gather round the CRT kids it's another story time from old man delni...

Back in the before times, Papa Delni setup an old 486 (actually 386 using a cyrix "486" cpu) as an X terminal. This was a hot setup with an ATI Graphics Wonder, AMD Lance network, 8mb of ram, the whole 9 yards.

Everything worked great except the network was terribly slow. Except when I moved the mouse, then it was nice and normal.

Turned out the network card and mouse were on the same IRQ, or maybe the driver was looking at the wrong IRQ, and the network buffers only got drained when the mouse was wiggled.

I actually used that little nugget of knowing things to know to switch to polled network buffers on a big fat firewall that was running freebsd -- it was constantly under huge load so there was no real advantage to waiting for IRQs.

Don't miss that world at all.

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Re:80286 ATX mainboard based on the IBM 5170 AT PC by crest on Wednesday November 13, 2024 @04:19PM (#42130111)

Oh yes `HZ=4000`, `net.link.ifqmaxlen=200`, `net.isr.dispatch=…`. I don't miss running out of hardware resources that would be a few 100 (or 1000) gates to get right like a nesting, vectored interrupt controller with enough sources and priorities.

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