Question

I need to read a floppy from a pre OS state and I have a function to read, but it cannot seem to read past the 4th sector...

void get_block(blk, buf) int blk; char buf[]
{
   int cyl, head, sector;

   cyl = ((blk*2) / 18) / 2;
   head = ((blk*2) / 18) % 2;
   sector = (blk*2) % 18;

   // Read first sector <<Dies here if blk > 2>>
   diskr(cyl, head, sector, buf);

   // Increment
   if ((sector = (++sector % 18)) == 0)
      if ((head = (++head % 2)) == 0)
         cyl++;

   // Read second sector <<Dies here if blk == 2>>
   diskr(cyl, head, sector, buf+512);
}

任何想法为什么? 我是否错误地将区块改成区?

Answer 1

如以下方案所示,假定磁盘为1.44M“氟”(80个气温器、2个头/圆筒、18个区/头、512个用药/部门)。

#include <stdio.h>
int main (void) {
    int blk, cyl, head, sector;
    for (blk = 0; blk <= 18; blk++) {
        cyl = ((blk*2) / 18) / 2;
        head = ((blk*2) / 18) % 2;
        sector = (blk*2) % 18;
        printf ("%2d (a) -> %2d %2d %2d", blk, cyl, head, sector);
        if ((sector = (++sector % 18)) == 0)
            if ((head = (++head % 2)) == 0)
                cyl++;
        printf (" (b) -> %2d %2d %2d
", cyl, head, sector);
    }
    return 0;
}

the output of which is:

 0 (a) ->  0  0  0 (b) ->  0  0  1
 1 (a) ->  0  0  2 (b) ->  0  0  3
 2 (a) ->  0  0  4 (b) ->  0  0  5
 3 (a) ->  0  0  6 (b) ->  0  0  7
 4 (a) ->  0  0  8 (b) ->  0  0  9
 5 (a) ->  0  0 10 (b) ->  0  0 11
 6 (a) ->  0  0 12 (b) ->  0  0 13
 7 (a) ->  0  0 14 (b) ->  0  0 15
 8 (a) ->  0  0 16 (b) ->  0  0 17
 9 (a) ->  0  1  0 (b) ->  0  1  1
10 (a) ->  0  1  2 (b) ->  0  1  3
11 (a) ->  0  1  4 (b) ->  0  1  5
12 (a) ->  0  1  6 (b) ->  0  1  7
13 (a) ->  0  1  8 (b) ->  0  1  9
14 (a) ->  0  1 10 (b) ->  0  1 11
15 (a) ->  0  1 12 (b) ->  0  1 13
16 (a) ->  0  1 14 (b) ->  0  1 15
17 (a) ->  0  1 16 (b) ->  0  1 17
18 (a) ->  1  0  0 (b) ->  1  0  1

I m a little 关切下列行为的不确定性质:

if ((sector = (++sector % 18)) == 0)

2. 建设,更喜欢:

if ((sector = (sector + 1) % 18)) == 0)

但是,如果给你以正确的价值观,那就应当是oka。但是,你需要检查它does。给你适当的数值。在我版本的<代码>gcc中这样做。并不意味着你会这样做。

或者,你只能使用上文所建议的表格,其中界定了is。

你的失败点是,你在头脑或气瓶之间交接的距离很近,因此,我不认为这是一个总结问题,但是,如果可能的话,你就应当勾画环境中的价值观。

When you say you "can t read past the 4th sector", you should specify exactly what that means? Does the machine freeze, do you get a disk error, does it return what you think is rubbish?

软磁盘可能无法正确格式,或者它有错,也有可能仅仅掌握你预期看到的数据。也许值得与监督事务司/Windows/whatever进行脱硫,并检查贵方案的内容。

友情链接