This quote, from Linux, was an early inspiration for linuxbios (now
coreboot). The idea was that the kernel could take on tasks that firmware
did, or at least ignore all the mistakes firmware made. For a time, we even
showed how to do real SMP startup in Linux, not firmware, until the K7 made
a mess of things. (today's SMP startup is not even close to what you really
have to do ...)
So in 1999 we envisioned a world in which the kernel took on more and more
startup tasks, and the firmware did less and less. Of course this is not
how it worked out. Linux is more dependent on firmware than ever. Firmware
(at least the UEFI kind) is as large and complex, at least, as Linux. In
fact in 4.x, Linux requires/assumes that the work defined below is done by
firmware or bootloader, or it will silently hang or fail on startup. It's
less capable than the Linux of the 90s. A pity.
This is from 2.2 arch/i386/entry.S
! well, that went ok, I hope. Now we have to reprogram the interrupts :-(
! we put them right after the intel-reserved hardware interrupts, at
! int 0x20-0x2F. There they won't mess up anything. Sadly IBM really
! messed this up with the original PC, and they haven't been able to
! rectify it afterwards. Thus the bios puts interrupts at 0x08-0x0f,
! which is used for the internal hardware interrupts as well. We just
! have to reprogram the 8259's, and it isn't fun.
mov al,#0x11 ! initialization sequence
out #0x20,al ! send it to 8259A-1
call delay
out #0xA0,al ! and to 8259A-2
call delay
mov al,#0x20 ! start of hardware int's (0x20)
out #0x21,al
call delay
mov al,#0x28 ! start of hardware int's 2 (0x28)
out #0xA1,al
call delay
mov al,#0x04 ! 8259-1 is master
out #0x21,al
call delay
mov al,#0x02 ! 8259-2 is slave
out #0xA1,al
call delay
mov al,#0x01 ! 8086 mode for both
out #0x21,al
call delay
out #0xA1,al
call delay
mov al,#0xFF ! mask off all interrupts for now
out #0xA1,al
call delay
mov al,#0xFB ! mask all irq's but irq2 which
out #0x21,al ! is cascaded
! Well, that certainly wasn't fun :-(. Hopefully it works, and we don't
! need no steenking BIOS anyway (except for the initial loading :-).
! The BIOS routine wants lots of unnecessary data, and it's less
! "interesting" anyway. This is how REAL programmers do it.
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