使用ATA/IDE PIO读取磁盘扇区时出现异常数据

Question

在读取磁盘扇区时，我得到了一些意外的数据。

我试图在没有内核的情况下读取磁盘数据，但得到了奇怪的数据。我有一个文件fs.img，并像使用qemu-system-i386 -drive file=fs.img,index=0,media=disk,format=raw,if=ide ......一样使用它

hd fs.img
00000000  01 02 03 04 05 06 07 08  09 0a 0b 0c 0d 0e 0f 10  |................|
00000010  00 01 02 03 02 01 00 00  00 00 00 00 00 00 00 00  |................|
00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00a00010  00 00 00 00 00                                    |.....|
00a00015

我得到的数据：

Addr 0x0: 40 14 00 10 00 00 3f 00  00 00 4d 30 30 20 20 20 
Addr 0x10: 20 20 20 20 03 00 04 2e  2b 20 20 45 55 48 52 44
Addr 0x20: 53 20 20 20 20 20 20 20  20 20 20 20 20 20 20 10
Addr 0x30: 01 00 00 00 00 07 14 10  3f c0 00 10 01 00 07 07
Addr 0x40: 03 78 78 78 78 00 00 00  00 00 00 00 00 00 00 00
Addr 0x50: f0 16 21 00 00 21 00 00  3f 00 00 00 00 01 00 00
Addr 0x60: 00 00 00 00 01 00 00 00  00 00 00 00 00 00 00 00
Addr 0x70: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
Addr 0x80: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
Addr 0x90: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00

读取扇区代码：

read_sector(0, 4, buffer);
#define ATA_BASE 0x1f0
void read_sector(uint addr, uint count, uchar *buffer) {
// FIXME: assert count <= 255
// TODO: wait for ready
uchar data;
// how many sector
data = count;
outb(ATA_BASE + 2, data);
// set addr
data = addr & 0xff;
outb(ATA_BASE + 3, data);
data = addr >> 8 & 0xff;
outb(ATA_BASE + 4, data);
data = addr >> 16 & 0xff;
outb(ATA_BASE + 5, data);
data = (addr >> 24 & 0x0f) | 0xe0;
outb(ATA_BASE + 6, data);
// read command
data = 0x20;
outb(ATA_BASE + 7, data);
// pool
data = inb(ATA_BASE + 7);
while ((data & 0x88) != 0x08) {
data = inb(ATA_BASE + 7);
}
// read data
int loop = count * 512;
ushort d;
int p = 0;
while (loop--) {
d = inw(ATA_BASE);
printf("%xs ", d);
buffer[p] = d;
p += 1;
}
printf("n");
}

若我把地址改为read，我得到的输出和以前一样。如果我使用文本文件作为磁盘映像，我会得到如下输出：

Addr 0x0: 40 02 00 10 00 00 3f 00  00 00 4d 30 30 20 20 20 
Addr 0x10: 20 20 20 20 03 00 04 2e  2b 20 20 45 55 48 52 44
Addr 0x20: 53 20 20 20 20 20 20 20  20 20 20 20 20 20 20 10
Addr 0x30: 01 00 00 00 00 07 02 10  3f e0 00 10 01 00 07 07
Addr 0x40: 03 78 78 78 78 00 00 00  00 00 00 00 00 00 00 00
Addr 0x50: f0 16 21 00 00 21 00 00  3f 00 00 00 00 01 00 00
Addr 0x60: 00 00 00 00 01 00 00 00  00 00 00 00 00 00 00 00

只有0x01和0x37已从0x14更改为0x02。

Answer 1

在读取扇区之前，我已经发送了一个IDENTITY命令。它返回意外的数据。

如果我删除IDENTIFY命令的调用，则数据是正确的。

更多信息：https://wiki.osdev.org/ATA_PIO_Mode#IDENTIFY_command