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| author | Joursoir <chat@joursoir.net> | 2021-10-01 12:09:16 +0000 |
|---|---|---|
| committer | Joursoir <chat@joursoir.net> | 2021-10-01 12:09:16 +0000 |
| commit | 1d47855c80b63176cd55980cf68d5c187c44a766 (patch) | |
| tree | 963c94c2ac5062337fd1b6537b670da4f7ca3676 | |
| parent | 4325278d89c54ada17ec51ac1462ec6f8ae673ee (diff) | |
| download | mfsos-1d47855c80b63176cd55980cf68d5c187c44a766.tar.gz mfsos-1d47855c80b63176cd55980cf68d5c187c44a766.tar.bz2 mfsos-1d47855c80b63176cd55980cf68d5c187c44a766.zip | |
x86/boot/setup: enable a20 line
| -rw-r--r-- | arch/x86/boot/setup.s | 45 |
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!" |