-/*
- * FAT Partition Boot Sector. Loaded at 0x7C00:
- * 8a pbs.s; 8l -o pbs -l -H3 -T0x7C00 pbs.8
- * Will load the target at LOADSEG*16+LOADOFF, so the target
- * should be probably be loaded with LOADOFF added to the
- * -Taddress.
- * If LOADSEG is a multiple of 64KB and LOADOFF is 0 then
- * targets larger than 64KB can be loaded.
- *
- * This code uses the traditional INT13 BIOS interface and can
- * therefore only access the first 8.4GB of the disc.
- *
- * It relies on the _volid field in the FAT header containing
- * the LBA of the root directory.
- */
#include "x16.h"
#include "mem.h"
-#define LOADSEG (0x10000/16) /* where to load code (64KB) */
-#define LOADOFF 0
-#define DIROFF 0x0200 /* where to read the root directory */
-
-/*
- * FAT directory entry.
- */
-#define Dname 0x00
-#define Dext 0x08
-#define Dattr 0x0B
-#define Dtime 0x16
-#define Ddate 0x18
-#define Dstart 0x1A
-#define Dlengthlo 0x1C
-#define Dlengthhi 0x1E
-
-#define Dirsz 0x20
-
-/*
- * Data is kept on the stack, indexed by rBP.
- */
-#define Xdap 0x00 /* disc address packet */
-#define Xrootsz 0x10 /* file data area */
-#define Xdrive 0x12 /* boot drive, passed by BIOS or MBR */
-#define Xtotal 0x14 /* sum of allocated data above */
+#define RELOC 0x7c00
TEXT _magic(SB), $0
BYTE $0xEB; BYTE $0x3C; /* jmp .+ 0x3C (_start0x3E) */
MTSR(rAX, rSS) /* 0000 -> rSS */
MTSR(rAX, rDS) /* 0000 -> rDS, source segment */
MTSR(rAX, rES)
- LWI(_magic-Xtotal(SB), rSP)
- MW(rSP, rBP) /* set the indexed-data pointer */
- SBPB(rDL, Xdrive) /* save the boot drive */
+ LWI(0x100, rCX)
+ LWI(RELOC, rSI)
+ MW(rSI, rSP)
+ LWI(_magic(SB), rDI)
+ CLD
+ REP; MOVSL /* MOV DS:[(E)SI] -> ES:[(E)DI] */
- /* booting from a CD starts us at 7C0:0. Move to 0:7C00 */
- PUSHR(rAX)
- LWI(_nxt(SB), rAX)
- PUSHR(rAX)
- BYTE $0xCB /* FAR RET */
-
-TEXT _nxt(SB), $0
- STI
+ PUSHA
+ MW(rSP, rBP)
- LWI(confidence(SB), rSI) /* for that warm, fuzzy feeling */
- CALL16(BIOSputs(SB))
+ PUSHR(rCX)
+ PUSHI(start16(SB))
+ BYTE $0xCB /* FAR RET */
- CALL16(dreset(SB))
+TEXT halt(SB), $0
+_halt:
+ JMP _halt
-_jmp00:
+TEXT start16(SB), $0
+ STI
+ LWI(hello(SB), rSI)
+ CALL16(print16(SB))
+ LWI(crnl(SB), rSI)
+ CALL16(print16(SB))
LW(_volid(SB), rAX) /* Xrootlo */
- LW(_volid+2(SB), rDX) /* Xroothi */
-
- LWI(_magic+DIROFF(SB), rBX)
- CALL16(BIOSread(SB)) /* read the root directory */
+ LW(_volid+2(SB), rBX) /* Xroothi */
+ PUSHR(rBP)
+ LW(_sectsize(SB), rCX)
+ SUB(rCX, rSP)
+ MW(rSP, rBP)
+ MW(rSP, rSI)
- LWI((512/Dirsz), rBX)
+_nextsect:
+ PUSHR(rAX)
+ CALL16(readsect16(SB))
+ OR(rAX, rAX)
+ JNE _halt
- LWI(_magic+DIROFF(SB), rDI) /* compare first directory entry */
+ LW(_sectsize(SB), rCX)
+ SHRI(5, rCX)
-_cmp00:
- PUSHR(rDI) /* save for later if it matches */
- LWI(bootfile(SB), rSI)
- LWI(Dattr, rCX)
+_nextdir:
+ PUSHR(rCX)
+ PUSHR(rSI) /* save for later if it matches */
+ LWI(bootname(SB), rDI)
+ LW(bootnamelen(SB), rCX)
+ CLD
REP
CMPSB
- POPR(rDI)
- JEQ _jmp02
+ POPR(rSI)
+ POPR(rCX)
+ JEQ _found
+ ADDI(0x20, rSI)
+ LOOP _nextdir
+ POPR(rAX)
+ ADDI(1, rAX)
+ ADC(rCX, rBX)
+ JMP _nextsect
- DEC(rBX)
- JEQ _jmp01
+_found:
+ PUSHR(rDX)
- ADDI(Dirsz, rDI)
- JMP _cmp00
-_jmp01:
- CALL16(buggery(SB))
+ CLR(rBX)
-_jmp02:
- CLR(rBX) /* a handy value */
LW(_rootsize(SB), rAX) /* calculate and save Xrootsz */
- LWI(Dirsz, rCX)
+ LWI(0x20, rCX)
MUL(rCX)
LW(_sectsize(SB), rCX)
PUSHR(rCX)
DIV(rCX)
PUSHR(rAX) /* Xrootsz */
- /*
- * rDI points to the matching directory entry.
- */
- LXW(Dstart, xDI, rAX) /* starting sector address */
+ LXW(0x1a, xSI, rAX) /* starting sector address */
DEC(rAX) /* that's just the way it is */
DEC(rAX)
LB(_clustsize(SB), rCL)
PUSHR(rAX) /* calculate how many sectors to read */
PUSHR(rDX)
- LXW(Dlengthlo, xDI, rAX)
- LXW(Dlengthhi, xDI, rDX)
+ LXW(0x1c, xSI, rAX)
+ LXW(0x1e, xSI, rDX)
LW(_sectsize(SB), rCX)
PUSHR(rCX)
DEC(rCX)
POPR(rCX) /* _sectsize(SB) */
DIV(rCX)
MW(rAX, rCX)
- POPR(rDX)
+ POPR(rBX)
POPR(rAX)
+ POPR(rDX)
- LWI(LOADSEG, rBX) /* address to load into (seg+offset) */
- MTSR(rBX, rES) /* seg */
- LWI(LOADOFF, rBX) /* offset */
-
-_readboot:
- CALL16(BIOSread(SB)) /* read the sector */
-
- LW(_sectsize(SB), rDI) /* bump addresses/counts */
- ADD(rDI, rBX)
- JCC _incsecno
-
- MFSR(rES, rDI) /* next 64KB segment */
- ADDI(0x1000, rDI)
- MTSR(rDI, rES)
-
-_incsecno:
- CLR(rDI)
- INC(rAX)
- ADC(rDI, rDX)
- LOOP _readboot
-
- LWI(LOADSEG, rDI) /* set rDS for loaded code */
- MTSR(rDI, rDS)
- FARJUMP16(LOADSEG, LOADOFF) /* no deposit, no return */
-
-TEXT buggery(SB), $0
- LWI(error(SB), rSI)
- CALL16(BIOSputs(SB))
-
-_wait:
- CLR(rAX) /* wait for almost any key */
- BIOSCALL(0x16)
+ LWI(RELOC, rSI)
+ PUSHR(rSI)
-_reset:
- CLR(rBX) /* set ES segment for BIOS area */
- MTSR(rBX, rES)
+_loadnext:
+ PUSHR(rCX)
+ PUSHR(rAX)
+ CALL16(readsect16(SB))
+ OR(rAX, rAX)
+ JNE _loaderror
+ POPR(rAX)
+ CLR(rCX)
+ ADDI(1, rAX)
+ ADC(rCX, rBX)
+ LW(_sectsize(SB), rCX)
+ ADD(rCX, rSI)
+ POPR(rCX)
+ LOOP _loadnext
+ CLI
+ RET
- LWI(0x0472, rBX) /* warm-start code address */
- LWI(0x1234, rAX) /* warm-start code */
- POKEW /* MOVW AX, ES:[BX] */
+_loaderror:
+ LWI(ioerror(SB), rSI)
+ CALL16(print16(SB))
+ CALL16(halt(SB))
- FARJUMP16(0xFFFF, 0x0000) /* reset */
+TEXT print16(SB), $0
+ PUSHA
+ CLR(rBX)
+_printnext:
+ LODSB
+ ORB(rAL, rAL)
+ JEQ _printret
+ LBI(0x0E, rAH)
+ BIOSCALL(0x10)
+ JMP _printnext
+_printret:
+ POPA
+ RET
/*
- * Read a sector from a disc. On entry:
- * rDX:rAX sector number
- * rES:rBX buffer address
- * For BIOSCALL(0x13):
- * rAH 0x02
- * rAL number of sectors to read (1)
- * rCH low 8 bits of cylinder
- * rCL high 2 bits of cylinder (7-6), sector (5-0)
- * rDH head
- * rDL drive
- * rES:rBX buffer address
+ * in:
+ * DL drive
+ * AX:BX lba32,
+ * 0000:SI buffer
*/
-TEXT BIOSread(SB), $0
- LWI(5, rDI) /* retry count (ATAPI ZIPs suck) */
-_retry:
- PUSHA /* may be trashed by BIOSCALL */
- PUSHR(rBX)
-
- LW(_trksize(SB), rBX)
- LW(_nheads(SB), rDI)
- IMUL(rDI, rBX)
- OR(rBX, rBX)
- JZ _ioerror
-
-_okay:
- DIV(rBX) /* cylinder -> rAX, track,sector -> rDX */
-
- MW(rAX, rCX) /* save cylinder */
- ROLI(0x08, rCX) /* swap rC[HL] */
- SHLBI(0x06, rCL) /* move high bits up */
-
- MW(rDX, rAX)
- CLR(rDX)
- LW(_trksize(SB), rBX)
-
- DIV(rBX) /* head -> rAX, sector -> rDX */
-
- INC(rDX) /* sector numbers are 1-based */
- ANDI(0x003F, rDX) /* should not be necessary */
- OR(rDX, rCX)
-
- MW(rAX, rDX)
- SHLI(0x08, rDX) /* form head */
- LBPB(Xdrive, rDL) /* form drive */
-
- POPR(rBX)
- LWI(0x0201, rAX) /* form command and sectors */
- BIOSCALL(0x13) /* CF set on failure */
- JCC _BIOSreadret
+TEXT readsect16(SB), $0
+ PUSHA
+ CLR(rCX)
- POPA
- DEC(rDI) /* too many retries? */
- JEQ _ioerror
+ PUSHR(rCX) /* qword lba */
+ PUSHR(rCX)
+ PUSHR(rBX)
+ PUSHR(rAX)
- CALL16(dreset(SB))
- JMP _retry
+ PUSHR(rCX) /* dword buffer */
+ PUSHR(rSI)
-_ioerror:
- LWI(ioerror(SB), rSI)
- CALL16(BIOSputs(SB))
- JMP _wait
+ INC(rCX)
+ PUSHR(rCX) /* word # of sectors */
-_BIOSreadret:
- POPA
- RET
+ PUSHI(0x0010) /* byte reserved, byte packet size */
-TEXT dreset(SB), $0
- PUSHA
- CLR(rAX) /* rAH == 0 == reset disc system */
- LBPB(Xdrive, rDL)
+ MW(rSP, rSI)
+ LWI(0x4200, rAX)
BIOSCALL(0x13)
- ORB(rAH, rAH) /* status (0 == success) */
+ JCC _readok
+ ADDI(0x10, rSP)
POPA
- JNE _ioerror
+ CLR(rAX)
+ DEC(rAX)
RET
-
-/*
- * Output a string to the display.
- * String argument is in rSI.
- */
-TEXT BIOSputs(SB), $0
- PUSHA
- CLR(rBX)
-_BIOSputs:
- LODSB
- ORB(rAL, rAL)
- JEQ _BIOSputsret
-
- LBI(0x0E, rAH)
- BIOSCALL(0x10)
- JMP _BIOSputs
-
-_BIOSputsret:
+_readok:
+ ADDI(0x10, rSP)
POPA
+ CLR(rAX)
RET
-/* "Bad format or I/O error\r\nPress almost any key to reboot..."*/
-TEXT error(SB), $0
- BYTE $'B'; BYTE $'a'; BYTE $'d'; BYTE $' ';
- BYTE $'f'; BYTE $'o'; BYTE $'r'; BYTE $'m';
- BYTE $'a'; BYTE $'t'; BYTE $' '; BYTE $'o';
- BYTE $'r'; BYTE $' ';
-/* "I/O error\r\nPress almost any key to reboot..." */
+TEXT bootnamelen(SB), $0
+ WORD $8
+TEXT bootname(SB), $0
+ BYTE $'9'; BYTE $'B'; BYTE $'O'; BYTE $'O';
+ BYTE $'T'; BYTE $'F'; BYTE $'A'; BYTE $'T';
+ BYTE $0
+
TEXT ioerror(SB), $0
- BYTE $'I'; BYTE $'/'; BYTE $'O'; BYTE $' ';
- BYTE $'e'; BYTE $'r'; BYTE $'r'; BYTE $'o';
- BYTE $'r'; BYTE $'\r';BYTE $'\n';
- BYTE $'P'; BYTE $'r'; BYTE $'e'; BYTE $'s';
- BYTE $'s'; BYTE $' '; BYTE $'a'; BYTE $' ';
- BYTE $'k'; BYTE $'e'; BYTE $'y';
- BYTE $' '; BYTE $'t'; BYTE $'o'; BYTE $' ';
- BYTE $'r'; BYTE $'e'; BYTE $'b'; BYTE $'o';
- BYTE $'o'; BYTE $'t';
- BYTE $'.'; BYTE $'.'; BYTE $'.';
- BYTE $'\z';
+ BYTE $'i'; BYTE $'/'; BYTE $'o'; BYTE $'-';
+ BYTE $'e'; BYTE $'r'; BYTE $'r'; BYTE $0
-#ifdef USEBCOM
-/* "B COM" */
-TEXT bootfile(SB), $0
- BYTE $'B'; BYTE $' '; BYTE $' '; BYTE $' ';
- BYTE $' '; BYTE $' '; BYTE $' '; BYTE $' ';
- BYTE $'C'; BYTE $'O'; BYTE $'M';
- BYTE $'\z';
-#else
-/* "9LOAD " */
-TEXT bootfile(SB), $0
- BYTE $'9'; BYTE $'L'; BYTE $'O'; BYTE $'A';
- BYTE $'D'; BYTE $' '; BYTE $' '; BYTE $' ';
- BYTE $' '; BYTE $' '; BYTE $' ';
- BYTE $'\z';
-#endif /* USEBCOM */
+TEXT hello(SB), $0
+ BYTE $'p'; BYTE $'b'; BYTE $'s'; BYTE $0
-/* "PBS..." */
-TEXT confidence(SB), $0
- BYTE $'P'; BYTE $'B'; BYTE $'S'; BYTE $'1';
- BYTE $'.'; BYTE $'.'; BYTE $'.';
- BYTE $'\z';
+TEXT crnl(SB), $0
+ BYTE $'\r'; BYTE $'\n'; BYTE $0
projects / plan9front.git / blobdiff