2 questions on bootsect.S

2 questions on bootsect.S

[ram]

Hi,

I was looking through the linux (2.5.56) arch/i386/boot/bootsect.S and was
puzzled about a couple of things:

1. Near line 221 we have:
        sread:  .word 0             # sectors read of current track
        head:   .word 0             # current head
        track:  .word 0             # current track

    However, since a diskette can have at most 2 heads, 80 tracks and 36 
sectors
    per track, why are these not bytes instead of words especially since 
space is
    at such a tight premium in this code ?

2. Near line 272 we have "movw    $7, %bx" but the documentation I've
     been able to find about the "int 0x13" BIOS call says that for service
     code 0xe (write character and advance cursor), it does not take an
     attribute byte input parameter but rather uses the existing 
attribute. Is
     this movw instruction superfluous ?

Thanks.

Ram

Re: 2 questions on bootsect.S

[Jack Dennon]

[-- Attachment #1: Type: text/plain, Size: 147 bytes --]

You may need some tools if you
decide to "bend it around." Attached
is a shell script and a little C program
that I use to mess with bootsect.S:



[-- Attachment #2: text.tmp --]
[-- Type: application/x-unknown-content-type-TMP_auto_file, Size: 904 bytes --]

Re: 2 questions on bootsect.S

[Jack Dennon]

[-- Attachment #1: Type: text/plain, Size: 84 bytes --]

Sorry, that was supposed to
attach in the clear as plain text.
Try one more time:



[-- Attachment #2: boot.txt --]
[-- Type: text/plain, Size: 904 bytes --]



#! /bin/bash
# asmboot.sh: assemble bootsect.S
cpp -traditional bootsect.S -o bootsect.ss
removebl < bootsect.ss > bootsect.s
as -aln=bootsect.lst -o bootsect.o bootsect.s

--------------------------------------------------------------
/* removebl.c: filter to remove blank lines
   ...well, most of them, leaves single blank lines in place
 */
#include <stdio.h>
#include <string.h>

#define MAXLINE 256
char line[MAXLINE];

/* getline: get line into s, return length */
int getline(char s[], int lim)
{
	int c, i;
	
	i = 0;
	while (--lim > 0 && (c = getchar()) != EOF
			 && c != '\n')
		s[i++] = c;
	if (c == '\n')
		s[i++] = c;
	s[i] = '\0';
	return i;
}

main()
{
	int c, i, length;
	int plength = 0;  /* previous line length */

	while ( (length = getline(line,MAXLINE)) > 0) {
		if (length > 1 || plength > 1) {
			for (i = 0; i < length; i++)
			putchar(line[i]);
		}
		plength = length;
	}
}