[src/trunk]: src/sys/arch/i386/stand/cdboot Add some illumination ...

[dsl <dsl%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/4183c3cb10dd
branches:  trunk
changeset: 748441:4183c3cb10dd
user:      dsl <dsl%NetBSD.org@localhost>
date:      Sat Oct 24 10:28:30 2009 +0000

description:
Add some illumination ...

diffstat:

 sys/arch/i386/stand/cdboot/cdboot.S |  14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)

diffs (63 lines):

diff -r c90692e181ba -r 4183c3cb10dd sys/arch/i386/stand/cdboot/cdboot.S
--- a/sys/arch/i386/stand/cdboot/cdboot.S       Sat Oct 24 06:36:39 2009 +0000
+++ b/sys/arch/i386/stand/cdboot/cdboot.S       Sat Oct 24 10:28:30 2009 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cdboot.S,v 1.8 2008/05/03 13:07:31 ad Exp $    */
+/*     $NetBSD: cdboot.S,v 1.9 2009/10/24 10:28:30 dsl Exp $   */
 
 /*-
  * Copyright (c) 2005 The NetBSD Foundation, Inc.
@@ -224,6 +224,8 @@
 boot_cdrom:
        movw    $str_banner, %si
        call    message
+
+/* Read volume descriptor sectors until Primary decriptor found */
        movl    $VD_LBA, %eax
 next_block:
        movb    $1, %dh                 /* Number of sectors to read */
@@ -238,6 +240,7 @@
        call    message
        jmp     panic
 
+/* Read all of root directory */
 pvd_found:
        movw    $PVD_ADDR+PVD_ROOT_DR, %bx
        movl    DR_EXTENT(%bx), %eax    /* LBA of the root directory */
@@ -246,6 +249,8 @@
        movb    %dl, %dh                /*  ... and load it to %dh */
        movl    $ROOTDIR_ADDR, %ebx
        call    read_sectors
+
+/* Scan directory entries searching for /boot */
 next_entry:
        cmpb    $0, DR_LEN(%bx)
        jz      last_entry
@@ -270,6 +275,7 @@
        call    message
        jmp     panic
 
+/* Found /boot, read contents to 0x1000:0 */
 load_loader:
        movl    DR_EXTENT(%bx), %eax
        movl    DR_DATA_LEN(%bx), %edx
@@ -278,6 +284,8 @@
        movb    %dl, %dh
        movl    $LOADER_ADDR, %ebx
        call    read_sectors
+
+/* Finally call into code of /boot */
        movl    $boot_params, %esi      /* Provide boot_params */
        xorl    %edx, %edx
        movb    boot_drive, %dl
@@ -297,8 +305,8 @@
  */
 read_sectors:
        pusha
-       movl    %eax, edd_lba           /* Convert LBA to segment */
-       shrl    $4, %ebx
+       movl    %eax, edd_lba
+       shrl    $4, %ebx                /* Convert buffer addr to seg:0 */
        movw    %bx, edd_segment
        movb    %dh, edd_nsecs
        movb    boot_drive, %dl