diff options
| -rw-r--r-- | sys/boot/i386/cdboot/cdboot.s | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/sys/boot/i386/cdboot/cdboot.s b/sys/boot/i386/cdboot/cdboot.s index ab959f4..69ac8d4 100644 --- a/sys/boot/i386/cdboot/cdboot.s +++ b/sys/boot/i386/cdboot/cdboot.s @@ -485,10 +485,17 @@ twiddle: push %ax # Save ret # -# Enable A20 +# Enable A20. Put upper limit on amount of time we wait for the +# keyboard controller to get ready (65K x ISA access time). If +# we wait more than that amount it's likely that the hardware +# is legacy-free and simply doesn't have keyboard controller +# and don't need enabling A20 at all. # seta20: cli # Disable interrupts -seta20.1: in $0x64,%al # Get status + xor %cx,%cx # Clear +seta20.1: inc %cx # Increment, overflow? + jz seta20.3 # Yes + in $0x64,%al # Get status test $0x2,%al # Busy? jnz seta20.1 # Yes mov $0xd1,%al # Command: Write @@ -498,7 +505,7 @@ seta20.2: in $0x64,%al # Get status jnz seta20.2 # Yes mov $0xdf,%al # Enable out %al,$0x60 # A20 - sti # Enable interrupts +seta20.3: sti # Enable interrupts ret # To caller # |
