PIT additions

Author: Ian Seyler

src/init/pit.asm

@@ -9,16 +9,59 @@
 init_pit:
 	; Enable PIT
 	; Base rate is 1193182 Hz
-	mov al, 0x36			; Channel 0 (7:6), Access Mode lo/hi (5:4), Mode 3 (3:1), Binary (0)
+	mov al, 0x34			; Channel 0 (7:6), Access Mode lo/hi (5:4), Mode 2 (3:1), Binary (0)
 	out 0x43, al
-	mov al, 0x3C			; 60
+	; Set divisor to 12 (1193182 Hz / 12 = ~99432 Hz)
+	; This gives a precision of ~10 microseconds
+	mov al, 0x74
 	out 0x40, al			; Set low byte of PIT reload value
 	mov al, 0x00
 	out 0x40, al			; Set high byte of PIT reload value
-	; New rate is 19866 Hz (1193182 / 60)
-	; 0.050286633812733 milliseconds (ms)
-	; 50.28663381273300814 microseconds (us)
+
+	; Create gate for PIT IRQ
+	mov edi, 0x20
+	mov eax, pit_irq
+	call create_gate
+
+	; Enable PIT Interrupt via the PIC
+	in al, 0x21
+	mov al, 11111110b		; Enable PIT
+	out 0x21, al
+
+	ret
+
+
+; -----------------------------------------------------------------------------
+; os_pit_delay -- Delay by X microseconds
+; IN:	RAX = Time microseconds
+; OUT:	All registers preserved
+; Note:	There are 1,000,000 microseconds in a second
+;	There are 1,000 milliseconds in a second
+os_pit_delay:
+	push rdx
+	push rcx
+	push rbx
+	push rax
+
+	; The PIT only gives us a precision of ~10 microseconds
+	; We need to divide RAX by 10
+	mov ecx, 10
+	xor edx, edx
+	div rcx
+
+	add rax, [p_Counter_Timer]
+
+os_pit_delay_loop:
+	mov rbx, [p_Counter_Timer]
+	cmp rax, rbx
+	jae os_pit_delay_loop
+
+	pop rax
+	pop rbx
+	pop rcx
+	pop rdx
 	ret
+; -----------------------------------------------------------------------------
 
 
 ; =============================================================================

src/init/smp.asm

@@ -7,6 +7,8 @@
 
 
 init_smp:
+	sti				; Enable interrupts in case PIT is needed
+
 	; Check if we want the AP's to be enabled.. if not then skip to end
 	cmp byte [cfg_smpinit], 1	; Check if SMP should be enabled
 	jne noMP			; If not then skip SMP init
@@ -50,7 +52,7 @@ smp_send_INIT_done:
 
 	; Wait 500 microseconds
 	mov eax, 500
-	call os_hpet_delay
+	call delay
 
 	mov esi, IM_DetectedCoreIDs
 	xor ecx, ecx
@@ -82,7 +84,7 @@ smp_send_SIPI_done:
 
 	; Wait 10000 microseconds for the AP's to finish
 	mov eax, 10000
-	call os_hpet_delay
+	call delay
 
 noMP:
 	; Gather and store the APIC ID of the BSP
@@ -100,7 +102,7 @@ noMP:
 	rdtsc
 	push rax
 	mov rax, 1024
-	call os_hpet_delay
+	call delay
 	rdtsc
 	pop rdx
 	sub rax, rdx
@@ -109,7 +111,35 @@ noMP:
 	div rcx
 	mov [p_cpu_speed], ax
 
+	cli				; Disable interrupts in case PIT was needed
+
+	ret
+
+
+; -----------------------------------------------------------------------------
+; delay -- Delay by X microseconds
+; IN:	RAX = Time microseconds
+; OUT:	All registers preserved
+; Note:	There are 1,000,000 microseconds in a second
+;	There are 1,000 milliseconds in a second
+delay:
+	push rax
+	push rbx
+
+	mov rbx, [p_HPET_Address]	; Was HPET detected?
+	cmp rbx, 0
+	je delay_pit			; If not, use PIT for timing
+	call os_hpet_delay
+	jmp delay_done
+
+delay_pit:
+	call os_pit_delay
+
+delay_done:
+	pop rbx
+	pop rax
 	ret
+; -----------------------------------------------------------------------------
 
 
 ; =============================================================================

src/interrupt.asm

@@ -23,6 +23,22 @@ interrupt_gate:				; handler for all other interrupts
 ; -----------------------------------------------------------------------------
 
 
+; -----------------------------------------------------------------------------
+; PIT interrupt. IRQ 0x00, INT 0x20
+align 16
+pit_irq:
+	push rax
+
+	inc qword [p_Counter_Timer]
+
+	mov al, 0x20			; Acknowledge the IRQ
+	out 0x20, al
+
+	pop rax
+	iretq
+; -----------------------------------------------------------------------------
+
+
 ; -----------------------------------------------------------------------------
 ; Floppy drive interrupt. IRQ 0x06, INT 0x26
 ; This IRQ runs when floppy drive reads from or writes to whole disk

src/pure64.asm

@@ -769,6 +769,9 @@ pde_end:
 	call debug_block
 %endif
 
+; Configure system timer
+; HPET is preferred but may not exist. If there was no ACPI table entry then use PIT
+
 	mov rax, [p_HPET_Address]
 	cmp rax, 0
 	jz skip_hpet