Re: IRQs

Richard B. Johnson (
Mon, 3 Mar 1997 21:18:54 -0500 (EST)

On Mon, 3 Mar 1997, Bob Welsh wrote:

> Hi,
> Quick question. Is it possible to selectively disable interrupts for a given
> IRQ in 386 architecture or can one only disable all interrupts. We are
> working on a device driver for a rather stupid device. As we are waiting for
> a register to clear on the device, it appears the device is interrupting and a
> new device command from the interrupt routine is reseting the register.
> Unfortunately disabling interrupts on the device also clears the register.
> Any suggestions?
> Bob Welsh
Shure can. The control port for the "low" IRQs is at 0x21 and the
"high" IRQs is at 0xA1. It is a bit-mapped mask, bit 0 is IRQ0 on
the low port. Bit 0 is IRQ8 on the high port (the interrupt controllers
are cascaded).. These ports are R/W, you can save the bits then put
them back the way they were.

Dick Johnson
Richard B. Johnson
Project Engineer
Analogic Corporation
Voice : (508) 977-3000 ext. 3754
Fax : (508) 532-6097
Modem : (508) 977-6870
Ftp :
Email :,
Penguin : Linux version 2.1.27 on an i586 machine (66.15 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.