Questions tagged [interrupt]

For questions regarding processor interrupt signals on retrocomputing hardware

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132 views

How did commercial GBA games sample the button state?

For the GBA, I am under the impression that there are two ways to detect a button event: Enable IRQs and set up a handler for the button event Check a button's state during the vblank period Which ...
6
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1answer
153 views

Chaining IRQ's with BASIC & Kernal routines turned off

Having disabled BASIC and Kernal routines I set up an IRQ to run the following code when the raster line reaches 200: .irq1 inc 53280 // change border colour // lda #$ff // clear the ...
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2answers
230 views

Z80: Interrupt (IM2) daisy chain for “foreign” peripherals

I'm looking for a way (apart from manually wiring up Fig.15 of The Z80 Family Program Interrupt Structure) to daisy chain "non-Z80-family" devices in an IM2 Z80 system i'm designing. So far ...
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2answers
1k views

BIOS interrupts vs Hardware interrupts

On an x86 chip running in Real Mode, interrupts are resolved with the help of the IVT (Interrupt Vector Table), which is an array located at address 0000h:0000h that consists of 256 entries, 32-bit ...
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0answers
97 views

Zenith Data Systems laptop with Timer Interrupt Error

I have an old Zenith “laptop” that runs on an 80c88 processor, and apparently was manufactured around 1985. It’s quite a beast of a laptop - size and weight, rather than computing power!. ...
6
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2answers
330 views

Were any M68000 systems capable of generating a “spurious interrupt”?

When an interrupt occurs on a Motorola 68000-family processor, it enters an interrupt acknowledge state, which continues until one of three signals are asserted: An external device places the ...
8
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2answers
251 views

(Lack of) identifying IRQ sources in C64 interrupt handlers

I'm trying to learn about C64 interrupt handling (with the goal of putting it in practice). My understanding is that interrupts can be triggered by different sources but there is only one interrupt ...
3
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4answers
641 views

Is the ZX Spectrum multithread capable? [closed]

I know the spectrum had the IM2 mode, but can I start multiple threads running simultaneously? Like to play sounds, watch the keyboard, and other tasks who can be runned simultaneous.
14
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2answers
812 views

Does the Z80 allow interrupts after processing and ignoring a 0xdd prefix?

I read here that if the Z80 encounters e.g. multiple 0xdd prefixes in sequence, for each 0xxdd except the last it acts almost like a NOP, but does not allow interrupts to occur immediately after "...
3
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2answers
289 views

What's the Motorola microprocessor with two sets of registers to avoid costly context switch?

I remember reading somewhere (maybe on Hacker News or Lobsters) that Motorola made a microprocessor some decades ago with two sets of registers. This means when handling an interrupt, it does not need ...
4
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2answers
264 views

6502 interrupts when RDY is low

If the NMI line goes from high to low when the RDY is low, is the NMI detected, so that when RDY goes high, NMI is performed ? Or is the NMI discarded when it occurs when RDY is low ? (In case of ...
7
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1answer
268 views

Importance of obeying Apple II IRQ priority

In the Apple II, DMA and IRQ priority is determined by a daisy-chain system, in which a card may only assert an IRQ or perform DMA when all higher-priority cards allow it. I understand the importance ...
14
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1answer
671 views

Why didn't Wozniak's interrupts work on the Apple I monitor program?

In his autobiography, Steve Wozniak recounts[1] his difficulty getting interrupts working on the 6502 microprocessor: The next step was to debug the 256-byte monitor program on the PROMs. I spent ...
17
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1answer
2k views

How does single-stepping on the 8086 interact with internal and external interrupts?

The 1979 version of the 8086 family user's manual is available at different places in the internet, see 1,2,3. It seems there is no newer version available. This manual documents the single-stepping ...
25
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3answers
4k views

What are uses of the byte after BRK instruction on 6502?

The BRK instruction on the MOS 6502 seems to be one of the more ill-documented features of the processor. The 1976 preliminary data sheet from MOS indicates that it's a 1-byte instruction using the &...
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7answers
2k views

8086 stack segment and avoiding overflow in interrupts

This is a followup to Could the Intel 8086 CPU have many segments in memory of the same type? In the event of a hardware interrupt or user interrupt through the INT instruction, was there a risk that ...
3
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3answers
414 views

Interrupt pin type on the 6502

I have a really basic question. I have to design an 65C02-based personal computer for a school project. I have to draw my own footprint for the 65C02. My question is what type of pin is the IRQB (...
19
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4answers
2k views

Did the IBM PC use the 8088's NMI line?

As I understand it, the Intel 8088 CPU used in the original IBM PC had two interrupt lines: INTR and NMI. INTR was fed from the Intel 8259 Programmable Interrupt Controller, which handled the IRQs ...
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4answers
2k views

How does the Z80 determine which peripheral sent an interrupt?

My understanding of how interrupts (and more specifically, interrupt daisy-chaining) works in the Z80 is limited, to say the least, so if I get anything wrong please correct me. Anyway, let's say I ...
7
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3answers
754 views

Why do we need to acknowledge the interrupt from VIC-II?

A page on how to do raster interrupts includes the following code Irq: LDA #7 STA $D020 ; Turn screen frame yellow LDX #90 Pause: DEX BNE Pause ; Empty loop that "...
2
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1answer
342 views

Is it possible to switch the interrupt source of the C64 to VIC without changing the IRQ routine?

The ROM IRQ routine at $EA31 is usually trigggered by the timer interrupt 60 times a second. Is it possible to switch the interrupt source to VIC and still use the same routine? If yes, which memory ...
4
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2answers
261 views

Does the Intersil 6100 do interrupts differently from other PDP-8s?

As I recall, the original PDP-8 actually does a jsr 0000 when an interrupt happens, so that the interrupt service routine started at address 0001. I think that saves a few gates, since the instruction ...
7
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5answers
718 views

What stops an IO device from driving the databus longer than the CPU expects?

For example, consider the case of handling an INT interrupt signal in the Z80. When the CPU makes the IORQ signal active, it expects the requesting IO device to place a vector onto on the databus. And ...
10
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3answers
2k views

Why do they use CLI in an IRQ routine?

I am studying an FLI routine in http://codebase64.org/doku.php?id=base:fli_displayer and I noticed that the CLI instruction is being used in this IRQ routine: irq0: pha ... cli ; &...
2
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4answers
746 views

Intel 8080 and Altair 8800. 256 I/0 ports, but only 7 free RST (interrupt subroutine) - how it works?

I have looked this video - Altair 8800 - Interrupt Acknowledge Cycle and have few questions (I have read wikipedia Intel 8080 article, Altair 8800 Operator's manual, Charles Petzold "Code" and few ...
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3answers
300 views

What is the FPD bit on the PDP-10?

When an interrupt happens on a PDP-10 right, as on many other architectures you get the program counter pushed onto the stack. Actually, the program counter includes many status bits in the upper half ...
3
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2answers
995 views

How can a C64 interrupt let the KERNAL keep operating?

I am working on a loading screen, and what I wanted was a simple raster trick (just change the border colour on the bottom half of the screen), and also call the KERNAL to load some more data from a ...
10
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2answers
1k views

Did the VIC-20 support raster scanline tricks like the Commodore 64?

I've been programming the C64 on/off for over 30 years (wow). However, I have a few VIC-20's I want to program. I never had a VIC-20 as a kid so I haven't had much exposure to them. Am I correct in ...
16
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1answer
350 views

Did any Mockingboard game use the VIA timers or interrupts?

There were only a small number of games that supported any of the Apple II sound cards such as the Mockingboard. From those games that used the Mockingboard, did any of them utilize the on-board VIA'...
11
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1answer
2k views

Timing interrupts on MS-DOS

On the ZX Spectrum, you get an interrupt every frame. As I recall, the operating system uses this to periodically scan the keyboard and probably other things also, but you can have your own routine ...