diff options
| -rw-r--r-- | sys/src/boot/pc/pbs.s | 26 | ||||
| -rw-r--r-- | sys/src/boot/pc/x16.h | 1 |
2 files changed, 16 insertions, 11 deletions
diff --git a/sys/src/boot/pc/pbs.s b/sys/src/boot/pc/pbs.s index bff333617..e79c61998 100644 --- a/sys/src/boot/pc/pbs.s +++ b/sys/src/boot/pc/pbs.s @@ -156,43 +156,47 @@ _nextdir: _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) diff --git a/sys/src/boot/pc/x16.h b/sys/src/boot/pc/x16.h index f0c9376dc..21edbac46 100644 --- 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; |