timer.c

/*
 * local apic (in x2apic mode) timer driver
 */
#include "printk.h"
#include "string.h"
#include <stdint.h>

/*
 * initialize the timer
 *
 * returns 0 if success else 1.
 */
int timer_init(void)
{
	int i;
	uint32_t msg1, msg2, msg3, value1, value2, value3;
	uint16_t cpuid_ax;
	char *gen_intel_msg = "GenuineIntel";

	/* check for the "GenuineIntel" message */
		__asm__("mov eax, 0\n\t"
			"cpuid\n\t"
			"mov %0, ebx\n\t"
			"mov %1, edx\n\t"
			"mov %2, ecx"
			::"m" (msg1),
			"m" (msg2),
			"m" (msg3):);
	
		for(i = 0; i < 4; i++) {
			if(strncmp(gen_intel_msg[i], (char) msg1, 1) !=0) {
				printk("error: timer: cpuid: processor is not genuine intel!\n");
				return 1;
			}
			msg1 >>= 8;
		}
	
		for(; i < 8; i++) {
			if(strncmp(gen_intel_msg[i], (char) msg2, 1) !=0) {
				printk("error: timer: cpuid: processor is not genuine intel!\n");
				return 1;
			}
			msg2 >>= 8;
		}
	
		for(; i < 12; i++) {
			if(strncmp(gen_intel_msg[i], (char) msg3, 1) !=0) {
				printk("error: timer: cpuid: processor is not genuine intel!\n");
				return 1;
			}
			msg3 >>= 8;
		}
	
	
		printk("@timer: cpuid: check for GenIntel message passed!\n");
	
		__asm__("mov eax, 0x1\n\t"
			"cpuid\n\t"
			"mov eax, 0x10\n\t"
			"mov ebx, 0x200000\n\t"
			"mov esi, edx\n\t"
			"and esi, 0x200\n\t"
			"and edx, eax\n\t"
			"and ecx, ebx\n\t"
			"mov %0, edx\n\t"
			"mov %1, ecx\n\t"
			"mov %2, esi"
			::"m" (value1),
			"m" (value2),
			"m" (value3):);
			
		/* check whether MSRs are supported */
		if (value1 == 0x10) {
			printk("@timer: cpuid: MSRs are supported!\n");
		} else if (value1 == 0x0) {
			printk("error: timer: cpuid: MSRs aren't supported!\n");
			return 1;
		}
	
		/* check whether the CPU has a built-in local APIC and if it hasn't been disabled in MSRs */
		if(value3 == 0x200) {
			printk("@timer: cpuid: the cpu has a built-in local apic!\n");
		} else {
			printk("error: timer: cpuid: either the cpu doesn't have a local apic or it has been disabled in MSRs!\n");
			return 1;
		}
	
		/* detecting x2APIC mode */
		if (value2 == 0x200000) {
			printk("@timer: cpuid: the processor supports the x2APIC capability!\n");
		} else if (value2 == 0x0) {
			printk("error: timer: cpuid: the processor doesn't support the x2APIC capability!\n");
			return 1;
		}
	
		/* enable the local apic */
		__asm__("mov ecx, 0x0\n\t"
			"mov ecx, 0x1b\n\t"
			"rdmsr\n\t"
			"or eax, 0x800\n\t"
			"wrmsr\n\t"
			"rdmsr\n\t"
			"and eax, 0x800\n\t"
			"mov %0, eax"
			::"m" (value1):);
		
		if (value1 == 0x800) {
			printk("@timer: init: enabled the local APIC!\n");
		} else {
			printk("error: timer: init: unable to enable the local APIC!\n");
			return 1;
		}
	
		/* enabling x2APIC mode */
		__asm__("mov ecx, 0x0\n\t"
			"mov ecx, 0x1b\n\t"
			"rdmsr\n\t"
			"or eax, 0x400\n\t"
			"wrmsr\n\t"
			"rdmsr\n\t"
			"and eax, 0xc00\n\t"
			"mov %0, eax"
			::"m" (value1):);
	
		if (value1 == 0xc00) {
			printk("@timer: init: enabled the local APIC in x2APIC mode!\n");
		} else {
			printk("error: timer: init: unable to enable the local APIC in x2APIC mode!\n");
			return 1;
		}
	
		/* get the lapic frequency equal to the core crystal's frequency */
		__asm__("mov eax, 0x16\n\t"
			"cpuid\n\t"
			"mov %0, ax"
			::"m" (cpuid_ax):);
	
		printk("@timer: cpuid: core base frequency is {d} MHz\n", cpuid_ax);

		return 0;
}

void set_divide_value(int value)
{
	__asm__("mov ecx, 0x0\n\t"
		"mov ecx, 0x83e\n\t"
		"rdmsr\n\t"
		"and eax, 0xfffffff4\n\t"
		"or eax, %0\n\t"
		"wrmsr"
		::"m" (value):);
}

/* returns 0 on success else 1 */
int set_mode(uint32_t mode)
{
	uint32_t res;

	__asm__("mov eax, 0x1\n\t"
		"cpuid\n\t"
		"and ecx, 0x1000000\n\t"
		"mov %0, ecx"
		::"m" (res):);	

	if(res == 0x1000000)
		printk("@ecx bit 24 is 1!\n");
	else if(res == 0x0) {
		printk("@ecx bit 24 is 0! not setting the mode using only the bit 17 at the moment!\n");
		return 1;
	}

	__asm__("mov ecx, 0x0\n\t"
		"mov ecx, 0x832\n\t"
		"rdmsr\n\t"
		"and eax, 0xfff9ffff\n\t"
		"or eax, %0\n\t"
		"wrmsr"
		::"m" (mode):);

	return 0;
}

void set_initial_count(uint32_t count, uint32_t mode)
{
	__asm__("mov ecx, 0x0\n\t"
		"mov ecx, 0x838\n\t"
		"mov eax, %0\n\t"
		"wrmsr"
		::"m" (count):);
}

uint32_t read_current_count(void)
{
	uint32_t count;

	__asm__("mov ecx, 0x0\n\t"
		"mov ecx, 0x839\n\t"
		"rdmsr\n\t"
		"mov %0, eax"
		::"m" (count):);

	return count;
}