ref: cd66b11f67654edfa54cab05422310d5c923784a
parent: d3b727db18c04b1eb485399dfcebff8ff61d8c7b
author: cinap_lenrek <cinap_lenrek@gmx.de>
date: Sun May 5 21:15:46 EDT 2013
pbs: allow 9bootfat start cluster beyond 0xFFFF pbs failed to load (silently loading garbage) 9BOOTFAT from start cluster beyond FFFF because we ignored the low word from the directory entry. now taking the high 16 bit of the directory's start cluster into account.
--- a/sys/src/boot/pc/pbs.s
+++ b/sys/src/boot/pc/pbs.s
@@ -156,43 +156,47 @@
_found:
CLR(rBX)
-
LW(_rootsize(SB), rAX) /* calculate and save Xrootsz */
LWI(0x20, rCX)
MUL(rCX)
LW(_sectsize(SB), rCX)
- PUSHR(rCX)
DEC(rCX)
ADD(rCX, rAX)
ADC(rBX, rDX)
- POPR(rCX) /* _sectsize(SB) */
+ INC(rCX)
DIV(rCX)
PUSHR(rAX) /* Xrootsz */
- LXW(0x1a, xSI, rAX) /* starting sector address */
- DEC(rAX) /* that's just the way it is */
- DEC(rAX)
- LB(_clustsize(SB), rCL)
- CLRB(rCH)
+ CLR(rCX)
+ LXW(0x1a, xSI, rAX) /* start cluster low */
+ LXW(0x14, xSI, rBX) /* start cluster high */
+ SUBI(2, rAX) /* cluster -= 2 */
+ SBB(rCX, rBX)
+
+ LB(_clustsize(SB), rCL) /* convert to sectors (AX:DX) */
+ IMUL(rCX, rBX)
MUL(rCX)
+ ADD(rBX, rDX)
+
LW(_volid(SB), rCX) /* Xrootlo */
ADD(rCX, rAX)
LW(_volid+2(SB), rCX) /* Xroothi */
ADC(rCX, rDX)
+
+ CLR(rBX)
POPR(rCX) /* Xrootsz */
ADD(rCX, rAX)
ADC(rBX, rDX)
- PUSHR(rAX) /* calculate how many sectors to read */
+ PUSHR(rAX) /* calculate how many sectors to read (CX) */
PUSHR(rDX)
LXW(0x1c, xSI, rAX)
LXW(0x1e, xSI, rDX)
LW(_sectsize(SB), rCX)
- PUSHR(rCX)
DEC(rCX)
ADD(rCX, rAX)
ADC(rBX, rDX)
- POPR(rCX) /* _sectsize(SB) */
+ INC(rCX)
DIV(rCX)
MW(rAX, rCX)
POPR(rBX)
--- a/sys/src/boot/pc/x16.h
+++ b/sys/src/boot/pc/x16.h
@@ -117,6 +117,7 @@
BYTE $i;
#define SHRBI(i, r) OPrr(0xC0, 0x05, r); /* r>>i -> r */ \
BYTE $i;
+#define SBB(r0, r1) OPrr(0x19, r0, r1) /* r1-r0 -> r1 */
#define SUB(r0, r1) OPrr(0x29, r0, r1) /* r1-r0 -> r1 */
#define SUBI(i, r) OP(0x81, 0x03, 0x05, r);/* r-i -> r */ \
WORD $i;
--
⑨