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authorJoursoir <chat@joursoir.net>2021-10-01 12:09:16 +0000
committerJoursoir <chat@joursoir.net>2021-10-01 12:09:16 +0000
commit1d47855c80b63176cd55980cf68d5c187c44a766 (patch)
tree963c94c2ac5062337fd1b6537b670da4f7ca3676 /arch/x86/boot/setup.s
parent4325278d89c54ada17ec51ac1462ec6f8ae673ee (diff)
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x86/boot/setup: enable a20 line
Diffstat (limited to 'arch/x86/boot/setup.s')
-rw-r--r--arch/x86/boot/setup.s45
1 files changed, 43 insertions, 2 deletions
diff --git a/arch/x86/boot/setup.s b/arch/x86/boot/setup.s
index bda71ee..a5c437c 100644
--- a/arch/x86/boot/setup.s
+++ b/arch/x86/boot/setup.s
@@ -15,6 +15,10 @@
.set CODESEG, gdt_code - gdt_start
.set DATASEG, gdt_data - gdt_start
+# Keyboard Controller commands:
+.set READ_OUTP, 0xD0 # Read Output Port
+.set WRITE_OUTP, 0xD1 # Write Output Port
+
.global _start # Make the symbol visible to ld
_start:
mov $SDATASEG, %ax
@@ -44,10 +48,32 @@ load_kernel: # Load our kernel
int $0x13 # Start reading from drive
jc disk_error # If carry flag set, bios failed to read
-switch_to_pm:
- BIOS_PRINT $boot_prot_mode_msg
cli # Switch of interrupt until we have set
# up the protected mode interrupt vector
+
+enable_a20:
+ BIOS_PRINT $enable_a20_msg
+
+ call wait_input
+ mov $READ_OUTP, %al
+ out %al, $0x64
+ call wait_output
+
+ in $0x60, %al # Read input buffer and store on stack
+ push %ax
+ call wait_input
+
+ mov $WRITE_OUTP, %al
+ out %al, $0x64
+ call wait_input
+
+ pop %ax # Pop the output port data from stack
+ or $2, %al # Set bit 1 (A20) to enable
+ out %al, $0x60 # Write the data to the output port
+ call wait_input
+
+switch_to_pm:
+ BIOS_PRINT $boot_prot_mode_msg
lgdt gdt_descriptor # Load our global descriptor table
mov %cr0, %eax # Set the first bit of CR0
@@ -63,6 +89,18 @@ disk_error:
BIOS_PRINT $disk_error_msg
jmp .
+wait_input:
+ in $0x64, %al # Read status
+ test $2, %al # Is input buffer full?
+ jnz wait_input # yes - continue waiting
+ ret
+
+wait_output:
+ in $0x64, %al
+ test $1, %al # Is output buffer full?
+ jz wait_output # no - continue waiting
+ ret
+
# Global Descriptor Table (contains 8-byte entries)
gdt_start:
gdt_null: # The mandatory null descriptor
@@ -109,6 +147,9 @@ boot_prot_mode_msg:
boot_load_kern_msg:
.asciz "Loading kernel into memory\r\n"
+enable_a20_msg:
+ .asciz "Enabling A20 line\r\n"
+
disk_error_msg:
.asciz "Disk read error!"