From e67aea1c0ccd3cc08a9110386d9b75b281941907 Mon Sep 17 00:00:00 2001
From: hpa <hpa>
Date: Sat, 14 Feb 1998 00:26:18 +0000
Subject: [PATCH] FAT16 support!!!

---
 NEWS         |  3 +++
 TODO         | 10 +++++++++-
 ldlinux.asm  | 36 ++++++++++++++++++++++++------------
 syslinux.asm |  7 -------
 syslinux.c   |  6 ++++++
 5 files changed, 42 insertions(+), 20 deletions(-)

diff --git a/NEWS b/NEWS
index ce73765..ff399e7 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,6 @@
+Changes in 1.32:
+	* FAT16 is now supported.
+
 Changes in 1.31:
 	* Now compiles under Linux, using NASM, rather than using
 	  Turbo Assembler under DOS.  See http://www.cryogen.com/Nasm
diff --git a/TODO b/TODO
index a296aa3..3c05d9e 100644
--- a/TODO
+++ b/TODO
@@ -1,6 +1,14 @@
 Currently scheduled for inclusion in 1.40:
 
-- FAT16 support (for LS120 floppies mainly).
+- FAT16 support (for LS120 floppies mainly).		DONE!
 - "Comboot" style boot files.
 - Booting DOS for a DOS/Linux dual rescue disk.
 - Cleaned up documentation, with a real man page.
+
+For a later release, perhaps:
+
+- Support for clusters larger than 16K.  This would require changing
+  a lot of the SYSLINUX internals so we can read partial clusters;
+  change the current "cluster pointers" to become
+  "cluster:sector pointers".
+
diff --git a/ldlinux.asm b/ldlinux.asm
index a6f04df..6e7328e 100644
--- a/ldlinux.asm
+++ b/ldlinux.asm
@@ -689,7 +689,8 @@ bootsignature	dw 0AA55h
 ldlinux_magic	db 'LDLINUX'
 missing_dot	db ' '
 		db 'SYS ', version_str, ' ', date
-magic_eof	db 0, 0Dh, 0Ah, 01Ah
+magic_eof	db 0, 
+crlf		db 0Dh, 0Ah, 0, 01Ah
 
 		align 4
 ldlinux_ent:
@@ -822,8 +823,6 @@ load_rest:
 ; All loaded up
 ;
 all_read_jmp:
-		mov si,copyright_str
-		call writestr
 		jmp all_read
 ;
 ; -----------------------------------------------------------------------------
@@ -945,13 +944,18 @@ nc_even:
 		pop ax
 nc_return:	ret
 
+;
+; FAT16 decoding routine.  Note that a 16-bit FAT can be up to 128K,
+; so we have to decide if we're in the "low" or the "high" 64K-segment...
+;
 nextcluster_fat16:
 		push ax
 		push ds
-		mov ax,(fat_seg >> 12)
+		mov ax,fat_seg
 		shl si,1
-		adc ax,byte 0
-		mov ds,ax
+		jnc .seg0
+		mov ax,fat_seg+1000h
+.seg0:		mov ds,ax
 		mov si,[si]
 		cmp si,0FFF0h
 		cmc
@@ -968,12 +972,6 @@ safedumpregs:
 		jmp dumpregs
 %endif
 
-;
-; Data that has to be in the first sector
-;
-copyright_str   db '  Copyright (C) 1994-', year, ' H. Peter Anvin'
-crlf		db 0Dh, 0Ah, 0
-
 rl_checkpt	equ $				; Must be <= 400h
 
 ; ----------------------------------------------------------------------------
@@ -982,6 +980,12 @@ rl_checkpt	equ $				; Must be <= 400h
 
 all_read:
 ;
+; Let the user (and programmer!) know we got this far.  This used to be
+; in Sector 1, but makes a lot more sense here.
+;
+		mov si,copyright_str
+		call writestr
+;
 ; Check that no moron is trying to boot Linux on a 286 or so.  According
 ; to Intel, the way to check is to see if the high 4 bits of the FLAGS
 ; register are either all stuck at 1 (8086/8088) or all stuck at 0
@@ -1041,6 +1045,7 @@ skip_checks:
 ; We still need to check if this is a 486 or higher, and if it isn't, blank
 ; out the WBINVD subroutine
 ;
+%if 0
 		pushfd
 		pushfd
 		pop eax
@@ -1055,6 +1060,11 @@ skip_checks:
 		jne is_486			; Is a 486 or higher, assume WBINVD works
 		mov word [flush_cache.wbinvd],09090h	; NOP out
 is_486:
+%else
+
+%define wbinvd	nop
+
+%endif
 
 ;
 ; Initialization that does not need to go into the any of the pre-load
@@ -2862,6 +2872,8 @@ lcase_tab       db 135, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138
 ;
 ; Various initialized or semi-initialized variables
 ;
+copyright_str   db '  Copyright (C) 1994-', year, ' H. Peter Anvin'
+		db 0Dh, 0Ah, 0
 boot_prompt	db 'boot: ',0
 wipe_char	db 08h, ' ', 08h, 0
 err_notfound	db 'Could not find kernel image: ',0
diff --git a/syslinux.asm b/syslinux.asm
index 92163b9..4082084 100644
--- a/syslinux.asm
+++ b/syslinux.asm
@@ -124,9 +124,6 @@ got_cmdline:
 		and al,al
 		jnz filesystem_error
 
-		cmp word [bx+dpbMaxCluster],4087 ; FAT16 not supported yet
-		ja fat16_error
-
 		cmp word [bx+dpbSectorSize],512	; Sector size = 512 required
 		jne sectorsize_error
 
@@ -139,9 +136,6 @@ hugeclust_error:
 filesystem_error:
 		mov dx,msg_filesystem_err
 		jmp die
-fat16_error:
-		mov dx,msg_fat16_err
-		jmp die
 sectorsize_error:
 		mov dx,msg_sectorsize_err
 		jmp die
@@ -262,7 +256,6 @@ die:
 		section .data
 msg_error:		db 'ERROR: $'
 msg_filesystem_err:	db 'Filesystem not found on disk', 0Dh, 0Ah, '$'
-msg_fat16_err:		db 'FAT16 filesystems not supported at this time', 0Dh, 0Ah, '$'
 msg_sectorsize_err:	db 'Sector sizes other than 512 bytes not supported', 0Dh, 0Ah, '$'
 msg_hugeclust_err:	db 'Clusters larger than 16K not supported', 0Dh, 0Ah, '$'
 msg_read_err:		db 'Disk read failed', 0Dh, 0Ah, '$'
diff --git a/syslinux.c b/syslinux.c
index 0a5afcc..8874d48 100644
--- a/syslinux.c
+++ b/syslinux.c
@@ -177,6 +177,12 @@ int main(int argc, char *argv[])
 		device);
 	exit(1);
       }
+    } else if ( !memcmp(sectbuf+bsFileSysType, "FAT16   ", 8) ) {
+      if ( clusters <= 4086 ) {
+	fprintf(stderr, "%s: ERROR: FAT16 but claims less than 4086 clusters\n",
+		device);
+	exit(1);
+      }
     } else {
       fprintf(stderr, "%s: filesystem type \"%8.8s\" not supported\n",
 	      device, sectbuf+bsFileSysType);
-- 
2.7.4