1 files changed, 162 insertions, 0 deletions
diff --git a/kernel/source/timer.asm b/kernel/source/timer.asm
new file mode 100644
index 0000000..d5f6f73
--- /dev/null
+++ b/kernel/source/timer.asm
@@ -0,0 +1,162 @@
+bits 64
+
+section .rodata
+
+section .text
+
+read_cmos_byte:
+;dil in = register number
+;al out = value
+;rdx and rcx are not touched
+
+  mov al, dil
+  out 0x70, al
+  in al, 0x71
+  ret
+
+global enable_rtc_interrupts
+enable_rtc_interrupts:
+
+  ;secondary status register
+  mov dil, 11
+  call read_cmos_byte
+
+  ;enable interrupts
+  or al, 0x40
+  mov cl, al
+
+  ;do cmos write
+  mov al, 11
+  out 0x70, al
+  mov al, cl
+  out 0x71, al
+
+  ret
+
+global acknowledge_rtc_interrupt
+acknowledge_rtc_interrupt:
+  mov dil, 12
+  jmp read_cmos_byte
+
+convert_bcd:
+;al in = byte (possibly bcd)
+;al out = byte (not bcd)
+;sil 0x02 = bcd
+;does not touch rdx, rcx, sil
+  test sil, 0x02
+  jz .no_convert
+
+  mov dil, al
+  and dil, 0xf0
+  and al, 0x0f
+  shr dil, 3
+  add al, dil
+  shl dil, 2
+  add al, dil
+
+.no_convert:
+  ret
+
+convert_hours:
+;al in = byte (possibly bcd and 12 hour)
+;al out = byte (not bcd or 12 hour)
+;sil 0x02 = bcd, sil 0x01 = 12 hour
+;does not touch rdx, rcx, sil
+  test sil, 0x01
+  jz convert_bcd
+
+  test al, 0x80
+  jz .am
+
+  and al, 0x7f
+  call convert_bcd
+  cmp al, 12
+  je .noon
+
+  add al, 12
+  ret
+
+.noon:
+  ret
+
+.am:
+  call convert_bcd
+  cmp al, 12
+  je .midnight
+
+  ret
+
+.midnight:
+  xor al, al
+  ret
+
+global get_time_from_rtc
+get_time_from_rtc:
+;rax out = time (see timer.cpp for encoding)
+;we assume the year is 20xx (sorry)
+
+  mov dil, 11
+  call read_cmos_byte
+
+  shr al, 1
+  not al
+  and al, 3
+  mov sil, al
+
+  xor rdx, rdx
+
+.outer_loop:
+  mov rcx, rdx
+
+.wait_for_update_loop:
+  ;status register - 0x80 is update in progress
+  mov dil, 10
+  call read_cmos_byte
+  test al, 0x80
+  jnz .wait_for_update_loop
+
+  ;years
+  mov dil, 9
+  call read_cmos_byte
+  call convert_bcd
+  mov dh, al
+
+  ;months
+  mov dil, 8
+  call read_cmos_byte
+  call convert_bcd
+  mov dl, al
+
+  shl edx, 16
+
+  ;days
+  mov dil, 7
+  call read_cmos_byte
+  call convert_bcd
+  mov dh, al
+
+  ;hours
+  mov dil, 4
+  call read_cmos_byte
+  call convert_hours
+  mov dl, al
+
+  shl rdx, 16
+
+  ;minutes
+  mov dil, 2
+  call read_cmos_byte
+  call convert_bcd
+  mov dh, al
+
+  ;seconds
+  xor dil, dil
+  call read_cmos_byte
+  call convert_bcd
+  mov dl, al
+
+  cmp rdx, rcx
+  jne .outer_loop
+
+  mov rax, rdx
+  ret