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/*
* Protected-mode bootstrap, to be jumped to by a Primary Bootstrap Sector.
* Load with -H3 -R4 -T0xNNNNNNNN to get a binary image with no header.
* Note that the processor is in 'real' mode on entry, so care must be taken
* as the assembler assumes protected mode, hence the sometimes weird-looking
* code to assure 16-bit instructions are issued.
*/
#include "mem.h"
#include "/sys/src/boot/pc/x16.h"
#undef BIOSCALL /* we don't know what evil the bios gets up to */
#define BIOSCALL(b) INT $(b); CLI
#define CMPL(r0, r1) BYTE $0x66; CMP(r0, r1)
#define LLI(i, rX) BYTE $0x66; /* i -> rX */ \
BYTE $(0xB8+rX); \
LONG $i;
/*
* Start:
* disable interrupts;
* set all segments;
* create temporary stack.
*/
TEXT _start16r(SB), $0
CLI /* interrupts off */
MFSR(rCS, rAX)
MTSR(rAX, rDS) /* set the data segment */
LWI(0, rAX) /* always put stack in first 64k */
MTSR(rAX, rSS)
LWI(PXEBASE, rSP) /* set the stack */
LWI(0x2401, rAX) /* enable a20 line */
BIOSCALL(0x15)
/*
* Do any real-mode BIOS calls before going to protected mode.
* Data will be stored at BIOSTABLES, not ROUND(end, BY2PG) as before.
*/
/*
* Check for CGA mode.
*/
_cgastart:
LWI(0x0F00, rAX) /* get current video mode in AL */
BIOSCALL(0x10)
ANDI(0x007F, rAX)
SUBI(0x0003, rAX) /* is it mode 3? */
JEQ _cgaputs
LWI(0x0003, rAX) /* turn on text mode 3 */
BIOSCALL(0x10)
_cgaputs: /* output a cheery wee message */
LWI(_hello(SB), rSI)
CLR(rBX)
_cgaputsloop:
LODSB
ORB(rAL, rAL)
JEQ _cgaend
LBI(0x0E,rAH)
BIOSCALL(0x10)
JMP _cgaputsloop
_cgaend:
/*
* Reset floppy disc system.
* If successful, make sure the motor is off.
*/
_floppystart:
CLR(rAX)
CLR(rDX)
BIOSCALL(0x13)
ORB(rAL, rAL)
JNE _floppyend
OUTPORTB(0x3F2, 0x00) /* turn off motor */
_floppyend:
LLI(BIOSTABLES, rAX) /* tables in low memory, not after end */
OPSIZE; ANDL $~(BY2PG-1), AX
OPSIZE; SHRL $4, AX
SW(rAX, _ES(SB))
CLR(rDI)
SW(rDI, _DI(SB))
MTSR(rAX, rES)
/*
* Check for APM1.2 BIOS support.
*/
LWI(0x5304, rAX) /* disconnect anyone else */
CLR(rBX)
BIOSCALL(0x15)
JCS _apmfail
LWI(0x5303, rAX) /* connect */
CLR(rBX)
CLC
BIOSCALL(0x15)
JCC _apmpush
_apmfail:
LW(_ES(SB), rAX) /* no support */
MTSR(rAX, rES)
LW(_DI(SB), rDI)
JCS _apmend
_apmpush:
OPSIZE; PUSHR(rSI) /* save returned APM data on stack */
OPSIZE; PUSHR(rBX)
PUSHR(rDI)
PUSHR(rDX)
PUSHR(rCX)
PUSHR(rAX)
LW(_ES(SB), rAX)
MTSR(rAX, rES)
LW(_DI(SB), rDI)
LWI(0x5041, rAX) /* first 4 bytes are APM\0 */
STOSW
LWI(0x004D, rAX)
STOSW
LWI(8, rCX) /* pop the saved APM data */
_apmpop:
POPR(rAX)
STOSW
LOOP _apmpop
_apmend:
/*
* Try to retrieve the 0xE820 memory map.
* This is weird because some BIOS do not seem to preserve
* ES/DI on failure. Consequently they may not be valid
* at _e820end:.
*/
SW(rDI, _DI(SB)) /* save DI */
CLR(rAX) /* write terminator */
STOSW
STOSW
CLR(rBX)
PUSHR(rBX) /* keep loop count on stack */
/* BX is the continuation value */
_e820loop:
POPR(rAX)
INC(rAX)
PUSHR(rAX) /* doesn't affect FLAGS */
CMPI(32, rAX) /* mmap[32+1] in C code */
JGT _e820pop
LLI(20, rCX) /* buffer size */
LLI(0x534D4150, rDX) /* signature - ASCII "SMAP" */
LLI(0x0000E820, rAX) /* function code */
BIOSCALL(0x15) /* writes 20 bytes at (es,di) */
JCS _e820pop /* some kind of error */
LLI(0x534D4150, rDX)
CMPL(rDX, rAX) /* verify correct BIOS version */
JNE _e820pop
LLI(20, rDX)
CMPL(rDX, rCX) /* verify correct count */
JNE _e820pop
SUBI(4, rDI) /* overwrite terminator */
LWI(0x414D, rAX) /* first 4 bytes are "MAP\0" */
STOSW
LWI(0x0050, rAX)
STOSW
ADDI(20, rDI) /* bump to next entry */
SW(rDI, _DI(SB)) /* save DI */
CLR(rAX) /* write terminator */
STOSW
STOSW
OR(rBX, rBX) /* zero if last entry */
JNE _e820loop
_e820pop:
POPR(rAX) /* loop count */
LW(_DI(SB), rDI)
CLR(rAX)
MTSR(rAX, rES)
_e820end:
/*
* Done with BIOS calls for now. realmode calls may use the BIOS later.
*/
/*
* Load a basic GDT to map 4GB, turn on the protected mode bit in CR0,
* set all the segments to point to the new GDT then jump to the 32-bit code.
*/
_real:
LGDT(_gdtptr16r(SB)) /* load a basic gdt */
MFCR(rCR0, rAX)
ORI(1, rAX)
MTCR(rAX, rCR0) /* turn on protected mode */
DELAY /* JMP .+2 */
LWI(SELECTOR(1, SELGDT, 0), rAX)/* set all segments */
MTSR(rAX, rDS)
MTSR(rAX, rES)
MTSR(rAX, rFS)
MTSR(rAX, rGS)
MTSR(rAX, rSS)
FARJUMP32(SELECTOR(2, SELGDT, 0), _start32p-KZERO(SB))
TEXT _hello(SB), $0
BYTE $'\r';
BYTE $'\n';
BYTE $'P'; BYTE $'l'; BYTE $'a'; BYTE $'n';
BYTE $' '; BYTE $'9'; BYTE $' '; BYTE $'f';
BYTE $'r'; BYTE $'o'; BYTE $'m'; BYTE $' ';
BYTE $'B'; BYTE $'e'; BYTE $'l'; BYTE $'l';
BYTE $' '; BYTE $'L'; BYTE $'a'; BYTE $'b';
BYTE $'s';
BYTE $'\z';
TEXT _DI(SB), $0
LONG $0
TEXT _ES(SB), $0
LONG $0