内存容量检查（1）

09_day/bootpack.c

@@ -3,6 +3,9 @@
 #include "bootpack.h"
 #include <stdio.h>
 
+unsigned int memtest(unsigned int start, unsigned int end);
+unsigned int memtest_sub(unsigned int start, unsigned int end);
+
 void HariMain(void)
 {
 	struct BOOTINFO *binfo = (struct BOOTINFO *) ADR_BOOTINFO;
@@ -20,6 +23,7 @@ void HariMain(void)
 	io_out8(PIC1_IMR, 0xef); /* 开放鼠标中断(11101111) */
 
 	init_keyboard();
+	enable_mouse(&mdec);
 
 	init_palette();
 	init_screen8(binfo->vram, binfo->scrnx, binfo->scrny);
@@ -30,7 +34,9 @@ void HariMain(void)
 	sprintf(s, "(%d, %d)", mx, my);
 	putfonts8_asc(binfo->vram, binfo->scrnx, 0, 0, COL8_FFFFFF, s);
 
-	enable_mouse(&mdec);
+	i = memtest(0x00400000, 0xbfffffff) / (1024 * 1024);
+	sprintf(s, "memory %dMB", i);
+	putfonts8_asc(binfo->vram, binfo->scrnx, 0, 32, COL8_FFFFFF, s);
 
 	for (;;) {
 		io_cli();
@@ -86,3 +92,65 @@ void HariMain(void)
 	}
 }
 
+#define EFLAGS_AC_BIT			0x00040000
+#define CR0_CACHE_DISABLE	0x60000000
+
+unsigned int memtest(unsigned int start, unsigned int end) 
+{
+	char flg486 = 0;
+	unsigned int eflg, cr0, i;
+
+	/* 确认CPU是386还是486以上的 */
+	eflg = io_load_eflags();
+	eflg |= EFLAGS_AC_BIT; /* AC-bit = 1 */
+	io_store_eflags(eflg);
+	eflg = io_load_eflags();
+	if ((eflg & EFLAGS_AC_BIT) != 0) {
+		/* 如果是386，即使设定AC=1，AC的值还会自动回到0 */
+		flg486 = 1;
+	}
+
+	eflg &= ~EFLAGS_AC_BIT; /* AC-bit = 0 */
+	io_store_eflags(eflg);
+
+	if (flg486 != 0) {
+		cr0 = load_cr0();
+		cr0 |= CR0_CACHE_DISABLE; /* 禁止缓存 */ 
+		store_cr0(cr0);
+	}
+
+	i = memtest_sub(start, end);
+
+	if (flg486 != 0) {
+		cr0 = load_cr0();
+		cr0 &= ~CR0_CACHE_DISABLE; /* 允许缓存 */
+		store_cr0(cr0);
+	}
+
+	return i;
+}
+
+unsigned int memtest_sub(unsigned int start, unsigned int end)
+{
+	unsigned int i, *p, old, pat0 = 0xaa55aa55, pat1 = 0x55aa55aa;
+	for (i = start; i <= end; i += 0x1000) {
+		p = (unsigned int *) (i + 0xffc);
+		old = *p; /* 先记住修改前的值 */
+		*p = pat0; /* 试写 */
+		*p ^= 0xffffffff; /* 反转 */
+		if (*p != pat1) { 
+			/* 检查反转结果 */
+			not_memory:
+			*p = old;
+			break;
+		}
+		*p ^= 0xffffffff; /* 再次反转 */
+		if (*p != pat0) { 
+			/* 检查值是否恢复 */
+			 goto not_memory;
+		}
+		*p = old; /* 恢复为修改前的值 */
+	}
+	return i;
+}
+

09_day/naskfunc.nas

@@ -11,6 +11,7 @@
 		GLOBAL	_io_out8, _io_out16, _io_out32
 		GLOBAL	_io_load_eflags, _io_store_eflags
 		GLOBAL	_load_gdtr, _load_idtr
+		GLOBAL	_load_cr0, _store_cr0
 		GLOBAL	_asm_inthandler21, _asm_inthandler27, _asm_inthandler2c
 		EXTERN	_inthandler21, _inthandler27, _inthandler2c
 
@@ -91,6 +92,15 @@ _load_idtr:		; void load_idtr(int limit, int addr);
 		LIDT	[ESP+6]
 		RET
 
+_load_cr0:		; int load_cr0(void);
+		MOV		EAX,CR0
+		RET
+
+_store_cr0:		; void store_cr0(int cr0);
+		MOV		EAX,[ESP+4]
+		MOV		CR0,EAX
+		RET
+
 _asm_inthandler21:
 		PUSH	ES
 		PUSH	DS