●memtest86+教學 Part7

這一次我想從簡單部份說起；學code得基本原則就是debug，因此要debug就必需將我們不懂的地方把它show到螢幕的畫面上。所以我們先介紹以下這個函式：
/*
* Print characters on screen
*/
void cprint(int y, int x, const char *text)
{
register int i;
char *dptr;

dptr = (char *)(SCREEN_ADR + (160*y) + (2*x));
for (i=0; text[i]; i++) {
*dptr = text[i];
dptr += 2;
}
tty_print_line(y, x, text);//印出的UART
}
這是一個印出文字(字串)到螢幕上的Routine，相信它應該非常簡單，SCREEN_ADR ：0xb8000，這個位址就是bios映射到vga的彩色文字資料區；對這一區的記憶體讀寫就等同於對螢目frame buffer讀寫；相關資訊可參考這個網址。
接著我們去回想一下do_test有呼叫一個routine：init()；
void init(void)
{
int i;

outb(0x8, 0x3f2); /* Kill Floppy Motor */

/* Turn on cache */
set_cache(1);

/* Setup the display */
display_init();

/* Determine the memory map */
if ((firmware == FIRMWARE_UNKNOWN) &&
(memsz_mode != SZ_MODE_PROBE)) {
if (query_linuxbios()) {
firmware = FIRMWARE_LINUXBIOS;
}
else if (query_pcbios()) {
firmware = FIRMWARE_PCBIOS;
}
}

mem_size();

/* setup pci */
pci_init();

/* setup beep mode */
beepmode = BEEP_MODE;

v->test = 0;
v->pass = 0;
v->msg_line = 0;
v->ecount = 0;
v->ecc_ecount = 0;
v->testsel = -1;
v->msg_line = LINE_SCROLL-1;
v->scroll_start = v->msg_line * 160;
v->erri.low_addr.page = 0x7fffffff;
v->erri.low_addr.offset = 0xfff;
v->erri.high_addr.page = 0;
v->erri.high_addr.offset = 0;
v->erri.min_bits = 32;
v->erri.max_bits = 0;
v->erri.min_bits = 32;
v->erri.max_bits = 0;
v->erri.maxl = 0;
v->erri.cor_err = 0;
v->erri.ebits = 0;
v->erri.hdr_flag = 0;
v->erri.tbits = 0;
for (i=0; tseq[i].msg != NULL; i++) {
tseq[i].errors = 0;
}
if (dmi_initialized) {
for (i=0; i <> 0) {
dmi_err_cnts[i] = 0;
}
}
}

cprint(LINE_CPU+1, 0, "L1 Cache: Unknown ");
cprint(LINE_CPU+2, 0, "L2 Cache: Unknown ");
cprint(LINE_CPU+3, 0, "Memory : ");
aprint(LINE_CPU+3, 10, v->test_pages);
cprint(LINE_CPU+4, 0, "Chipset : ");

cpu_type();

/* Find the memory controller (inverted from standard) */
find_controller();

if (v->rdtsc) {
cacheable();
cprint(LINE_TIME, COL_TIME+4, ": :");
}
cprint(0, COL_MID,"Pass %");
cprint(1, COL_MID,"Test %");
cprint(2, COL_MID,"Test #");
cprint(3, COL_MID,"Testing: ");
cprint(4, COL_MID,"Pattern: ");
cprint(LINE_INFO-2, 0, " WallTime Cached RsvdMem MemMap Cache ECC Test Pass Errors ECC Errs");
cprint(LINE_INFO-1, 0, " --------- ------ ------- -------- ----- --- ---- ---- ------ --------");
cprint(LINE_INFO, COL_TST, " Std");
cprint(LINE_INFO, COL_PASS, " 0");
cprint(LINE_INFO, COL_ERR, " 0");
cprint(LINE_INFO+1, 0, " -----------------------------------------------------------------------------");

for(i=0; i < style="font-weight: bold;">cprint(i, COL_MID-2, " ");
}
footer();
// Default Print Mode
// v->printmode=PRINTMODE_SUMMARY;
v->printmode=PRINTMODE_ADDRESSES;
v->numpatn=0;
find_ticks();
}
這些粗體字就是我會講解的重點；首先說明set_cache
void set_cache(int val)
{
extern struct cpu_ident cpu_id;//cpu_id這個資料結構在head.S中已初始化完成。
/* 386's don't have a cache */
if ((cpu_id.cpuid lss 1) && (cpu_id.type == 3))
{
cprint(LINE_INFO, COL_CACHE, "none");
return;
}
switch(val)
{
case 0:
cache_off();
cprint(LINE_INFO, COL_CACHE, "off");
break;
case 1:
cache_on();
cprint(LINE_INFO, COL_CACHE, " on");
break;
}
}

static inline void cache_on(void)
{
asm(
"push %eax\n\t"
"movl %cr0,%eax\n\t"
"andl $0x9fffffff,%eax\n\t" /* Clear CD and NW */
"movl %eax,%cr0\n\t"
"pop %eax\n\t");
}
這個組合語言是GCC-Inline-Assembly，請自行參考語法說明。打開CACHE快取才可使CPU存取RAM的速度加快；因為匯流排，即使是跑DUAL CHENNEL，也不會比CPU快，因此快取越大，更能提升CPU效能。但要知道一點，這軟體主要是測試記憶體，萬一CPU快取本身有問題，就很難去測試記憶體真正的PASS或FAIL。