Reprogramming the PIC

[K.J.]

I heard that if you are making a PMode OS that you should reprogram the PIC. Is this true, and if so why?

Thanks in advance,
K.J.

[roswell]

You must program the pic in order to avoid two interrupts to be on the same number.

Under real mode, hardware interrupts are mapped in range 0->31 if I have a good memory.

Under protected mode, Intel has "reserved" this range for exception.

So you have to re-program the pic to put the hardware interrupts away from Intel's garden.

You just have to change the offset of each PIC.

ROSWELL

PS : Sorry for my english but I'm french.

[K.J.]

Okay, so if I don't remap it then I get interrupts that don't work right? If all I want to do is just use the keyboard do I have to remap the PIC?

K.J.

[df]

under real mode you have int 0-7 and 70-78. the common thing to do is remap everything from 0-31.

check the os faq

http://www.mega-tokyo.com/os/os-faq-pics.html#remap_pic