Messages in this thread Patch in this message |  | | From | Robert Kaiser <> | Subject | Re: setup.S: A20 enable sequence (once again) | Date | Mon, 6 Nov 2000 21:20:46 +0100 |
| |
On Mon, 06 Nov 2000 you wrote: H. Peter Anvin wrote > I just looked at the code, and it's worse than I first thought: if > memory location 0x200 happens to contain 0x0001 when the kernel is > entered, this code with loop indefinitely.
Ooops, you're right !
How about this one:
diff -ur linux-2.4.0-test10/arch/i386/boot/setup.S linux/arch/i386/boot/setup.S --- linux-2.4.0-test10/arch/i386/boot/setup.S Mon Oct 30 23:44:29 2000 +++ linux/arch/i386/boot/setup.S Mon Nov 6 21:14:45 2000 @@ -631,6 +631,26 @@ # appropriate # that was painless, now we enable a20 +# Try the "fast A20" version first: +# You must preserve the other bits here. Otherwise embarrasing things +# like laptops powering off on boot happen. Corrected version by Kira +# Brown from Linux 2.2 +# + inb $0x92, %al # + orb $02, %al # "fast A20" version + andb $0xfe, %al # be sure not to reset CPU + outb %al, $0x92 # some chips have only this + +# See if that already did the job, skip keyboard controller +# accesses if so: some boards do not have a keyboard controller. +# These boards (especially if running on a slowish 386 EX) +# can spend several *minutes* in silence, polling for the +# non-existent keyboard controller. + + movw $0x100,%cx # small retry count + call a20_check + jne a20_enabled + call empty_8042 movb $0xD1, %al # command write @@ -641,20 +661,20 @@ outb %al, $0x60 call empty_8042 -# -# You must preserve the other bits here. Otherwise embarrasing things -# like laptops powering off on boot happen. Corrected version by Kira -# Brown from Linux 2.2 -# - inb $0x92, %al # - orb $02, %al # "fast A20" version - outb %al, $0x92 # some chips have only this - # wait until a20 really *is* enabled; it can take a fair amount of # time on certain systems; Toshiba Tecras are known to have this # problem. The memory location used here (0x200) is the int 0x80 # vector, which should be safe to use. +a20_recheck: + movw $0xffff,%cx # large retry count + call a20_check + jne a20_enabled + jmp a20_recheck # loop until no longer aliased + +# +# cx has retry count +a20_check: xorw %ax, %ax # segment 0x0000 movw %ax, %fs decw %ax # segment 0xffff (HMA) @@ -663,9 +683,11 @@ incw %ax # unused memory location <0xfff0 movw %ax, %fs:(0x200) # we use the "int 0x80" vector cmpw %gs:(0x210), %ax # and its corresponding HMA addr - je a20_wait # loop until no longer aliased + loopz a20_wait + ret # make sure any possible coprocessor is properly reset.. +a20_enabled: xorw %ax, %ax outb %al, $0xf0 call delay ---------------------------------------------------------------- Robert Kaiser email: rkaiser@sysgo.de SYSGO RTS GmbH Am Pfaffenstein 14 phone: (49) 6136 9948-762 D-55270 Klein-Winternheim / Germany fax: (49) 6136 9948-10 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
|  |