Add Programmable Interval Timer support

Add uptime command

src/commands.asm

@@ -4,6 +4,7 @@ sysinfo_command_str db 'sysinfo', 0
 reboot_command_str db 'reboot', 0
 clear_command_str db 'clear', 0
 help_command_str db 'help', 0
+uptime_command_str db 'uptime', 0
 
 STRING sysinfo_vendor_id, "Vendor ID: "
 STRING sysinfo_stepping, "Stepping: "
@@ -25,6 +26,7 @@ STRING sysinfo_ht, "ht "
 STRING sysinfo_fpu, "fpu "
 STRING sysinfo_aes, "aes "
 
+STRING uptime_message, "Uptime (s): "
 STRING available_commands, "Available commands: "
 STRING tab, "  "
 
@@ -42,6 +44,9 @@ command_table:
     dq clear_command_str
     dq clear_command
 
+    dq uptime_command_str
+    dq uptime_command
+
     dq help_command_str
     dq help_command
 
@@ -333,6 +338,22 @@ help_command:
 
     ret
 
+uptime_command:
+    push r8
+    push r9
+
+    mov r8, uptime_message
+    mov r9, uptime_message_length
+    call print_normal
+
+    mov r8, [timer_seconds]
+    call print_int_normal
+
+    pop r9
+    pop r8
+
+    ret
+
 reboot_command:
     ; Reboot using the 8042 keyboard controller
     ; by pulsing the CPU's reset pin

src/kernel.asm

@@ -97,6 +97,8 @@ lm_start:
 
     sti
 
+    call install_timer
+
     ; Enter the shell
     call shell_start
 
@@ -107,6 +109,7 @@ lm_start:
 %include "src/utils/macros.asm"
 %include "src/utils/console.asm"
 
+%include "src/timer.asm"
 %include "src/interrupts.asm"
 %include "src/shell.asm"
 

src/timer.asm

@@ -0,0 +1,47 @@
+
+install_timer:
+    mov r8, 1193180 / 1000
+
+    mov al, 0x36
+    out 0x43, al ; Command byte
+
+    mov rax, r8
+    out 0x40, al ; low bytes of divisor
+
+    mov rax, r8
+    shr rax, 8
+    out 0x40, al ; high bytes of divisor
+
+    mov r8, 0
+    mov r9, irq_timer_handler
+    call register_irq_handler
+
+    ret
+
+irq_timer_handler:
+    push rax
+
+    mov rax, [timer_ticks]
+    inc rax
+    mov [timer_ticks], rax
+
+    xor rdx, rdx
+    mov rcx, 1000
+    div rcx
+    cmp rdx, 0
+    jnz .end
+
+    mov rax, [timer_seconds]
+    inc rax
+    mov [timer_seconds], rax
+
+    .end:
+
+    pop r8
+
+    ret
+
+; Variables
+
+timer_ticks dq 0
+timer_seconds dq 0