My apologies for the base64-encoded patch; I didn't realize Mozilla
pulled that kind of mess for plain textfiles. Here it is again,
inline.
-hpa
--- arch/i386/boot/setup.S.old Fri Aug 10 15:20:51 2001
+++ arch/i386/boot/setup.S Fri Aug 10 17:05:27 2001
@@ -253,6 +253,7 @@
call prtstr
no_sig_loop:
+ hlt
jmp no_sig_loop
good_sig:
@@ -641,18 +642,40 @@
movw %ax, %ds
movw %dx, %ss
end_move_self: # now we are at the right place
- lidt idt_48 # load idt with 0,0
- xorl %eax, %eax # Compute gdt_base
- movw %ds, %ax # (Convert %ds:gdt to a linear ptr)
- shll $4, %eax
- addl $gdt, %eax
- movl %eax, (gdt_48+2)
- lgdt gdt_48 # load gdt with whatever is
- # appropriate
-# that was painless, now we enable a20
+#
+# Enable A20. This is at the very best an annoying procedure.
+# A20 code ported from SYSLINUX 1.52-1.63 by H. Peter Anvin.
+#
+
+A20_TEST_LOOPS = 32 # Iterations per wait
+A20_ENABLE_LOOPS = 255 # Total loops to try
+
+
+a20_try_loop:
+
+ # First, see if we are on a system with no A20 gate.
+a20_none:
+ call a20_test
+ jnz a20_done
+
+ # Next, try the BIOS (INT 0x15, AX=0x2401)
+a20_bios:
+ movw $0x2401, %ax
+ pushfl # Be paranoid about flags
+ int $0x15
+ popfl
+
+ call a20_test
+ jnz a20_done
+
+ # Try enabling A20 through the keyboard controller
+a20_kbc:
call empty_8042
+ call a20_test # Just in case the BIOS worked
+ jnz a20_done # but had a delayed reaction.
+
movb $0xD1, %al # command write
outb %al, $0x64
call empty_8042
@@ -661,29 +684,62 @@
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.
-
- xorw %ax, %ax # segment 0x0000
- movw %ax, %fs
- decw %ax # segment 0xffff (HMA)
- movw %ax, %gs
-a20_wait:
- 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
+ # 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.
+a20_kbc_wait:
+ xorw %cx, %cx
+a20_kbc_wait_loop:
+ call a20_test
+ jnz a20_done
+ loop a20_kbc_wait_loop
+
+ # Final attempt: use "configuration port A"
+a20_fast:
+ inb $0x92, %al # Configuration Port A
+ orb $0x02, %al # "fast A20" version
+ andb $0xFE, %al # don't accidentally reset
+ outb %al, $0x92
+
+ # Wait for configuration port A to take effect
+a20_fast_wait:
+ xorw %cx, %cx
+a20_fast_wait_loop:
+ call a20_test
+ jnz a20_done
+ loop a20_fast_wait_loop
+
+ # A20 is still not responding. Try frobbing it again.
+ #
+ decb (a20_tries)
+ jnz a20_try_loop
+
+ movw $a20_err_msg, %si
+ call prtstr
+
+a20_die:
+ hlt
+ jmp a20_die
+
+a20_tries:
+ .byte A20_ENABLE_LOOPS
+
+a20_err_msg:
+ .ascii "linux: fatal error: A20 gate not responding!"
+ .byte 13, 10, 0
+
+ # If we get here, all is good
+a20_done:
+
+# set up gdt and idt
+ lidt idt_48 # load idt with 0,0
+ xorl %eax, %eax # Compute gdt_base
+ movw %ds, %ax # (Convert %ds:gdt to a linear ptr)
+ shll $4, %eax
+ addl $gdt, %eax
+ movl %eax, (gdt_48+2)
+ lgdt gdt_48 # load gdt with whatever is
+ # appropriate
# make sure any possible coprocessor is properly reset..
xorw %ax, %ax
@@ -839,6 +895,37 @@
bootsect_panic_mess:
.string "INT15 refuses to access high mem, giving up."
+
+
+# This routine tests whether or not A20 is enabled. If so, it
+# exits with zf = 0.
+#
+# The memory address used, 0x200, is the int $0x80 vector, which
+# should be safe.
+
+A20_TEST_ADDR = 4*0x80
+
+a20_test:
+ pushw %cx
+ pushw %ax
+ xorw %cx, %cx
+ movw %cx, %fs # Low memory
+ decw %cx
+ movw %cx, %gs # High memory area
+ movw $A20_TEST_LOOPS, %cx
+ movw %fs:(A20_TEST_ADDR), %ax
+ pushw %ax
+a20_test_wait:
+ incw %ax
+ movw %ax, %fs:(A20_TEST_ADDR)
+ call delay # Serialize and make delay constant
+ cmpw %gs:(A20_TEST_ADDR+0x10), %ax
+ loope a20_test_wait
+
+ popw %fs:(A20_TEST_ADDR)
+ popw %ax
+ popw %cx
+ ret
# This routine checks that the keyboard command queue is empty
# (after emptying the output buffers)
-- <hpa@transmeta.com> at work, <hpa@zytor.com> in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt <amsp@zytor.com> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Wed Aug 15 2001 - 21:00:36 EST