diff options
Diffstat (limited to 'contrib/syslinux-4.02/gpxe/src/arch/i386/prefix/dskprefix.S')
| -rw-r--r-- | contrib/syslinux-4.02/gpxe/src/arch/i386/prefix/dskprefix.S | 381 |
1 files changed, 381 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/gpxe/src/arch/i386/prefix/dskprefix.S b/contrib/syslinux-4.02/gpxe/src/arch/i386/prefix/dskprefix.S new file mode 100644 index 0000000..60d351f --- /dev/null +++ b/contrib/syslinux-4.02/gpxe/src/arch/i386/prefix/dskprefix.S @@ -0,0 +1,381 @@ +/* NOTE: this boot sector contains instructions that need at least an 80186. + * Yes, as86 has a bug somewhere in the valid instruction set checks. + * + */ + +/* floppyload.S Copyright (C) 1991, 1992 Linus Torvalds + * modified by Drew Eckhardt + * modified by Bruce Evans (bde) + * + * floppyprefix.S is loaded at 0x0000:0x7c00 by the bios-startup routines. + * + * It then loads the system at SYSSEG<<4, using BIOS interrupts. + * + * The loader has been made as simple as possible, and continuous read errors + * will result in a unbreakable loop. Reboot by hand. It loads pretty fast by + * getting whole tracks at a time whenever possible. + */ + +FILE_LICENCE ( GPL2_ONLY ) + +.equ BOOTSEG, 0x07C0 /* original address of boot-sector */ + +.equ SYSSEG, 0x1000 /* system loaded at SYSSEG<<4 */ + + .org 0 + .arch i386 + .text + .section ".prefix", "ax", @progbits + .code16 + + jmp $BOOTSEG, $go /* reload cs:ip to match relocation addr */ +go: + movw $0x2000-12, %di /* 0x2000 is arbitrary value >= length */ + /* of bootsect + room for stack + 12 for */ + /* saved disk parm block */ + + movw $BOOTSEG, %ax + movw %ax,%ds + movw %ax,%es + movw %ax,%ss /* put stack at BOOTSEG:0x4000-12. */ + movw %di,%sp + +/* Many BIOS's default disk parameter tables will not recognize multi-sector + * reads beyond the maximum sector number specified in the default diskette + * parameter tables - this may mean 7 sectors in some cases. + * + * Since single sector reads are slow and out of the question, we must take care + * of this by creating new parameter tables (for the first disk) in RAM. We + * will set the maximum sector count to 36 - the most we will encounter on an + * ED 2.88. High doesn't hurt. Low does. + * + * Segments are as follows: ds=es=ss=cs - BOOTSEG + */ + + xorw %cx,%cx + movw %cx,%es /* access segment 0 */ + movw $0x78, %bx /* 0:bx is parameter table address */ + pushw %ds /* save ds */ +/* 0:bx is parameter table address */ + ldsw %es:(%bx),%si /* loads ds and si */ + + movw %ax,%es /* ax is BOOTSECT (loaded above) */ + movb $6, %cl /* copy 12 bytes */ + cld + pushw %di /* keep a copy for later */ + rep + movsw /* ds:si is source, es:di is dest */ + popw %di + + movb $36,%es:4(%di) + + movw %cx,%ds /* access segment 0 */ + xchgw %di,(%bx) + movw %es,%si + xchgw %si,2(%bx) + popw %ds /* restore ds */ + movw %di, dpoff /* save old parameters */ + movw %si, dpseg /* to restore just before finishing */ + pushw %ds + popw %es /* reload es */ + +/* Note that es is already set up. Also cx is 0 from rep movsw above. */ + + xorb %ah,%ah /* reset FDC */ + xorb %dl,%dl + int $0x13 + +/* Get disk drive parameters, specifically number of sectors/track. + * + * It seems that there is no BIOS call to get the number of sectors. Guess + * 36 sectors if sector 36 can be read, 18 sectors if sector 18 can be read, + * 15 if sector 15 can be read. Otherwise guess 9. + */ + + movw $disksizes, %si /* table of sizes to try */ + +probe_loop: + lodsb + cbtw /* extend to word */ + movw %ax, sectors + cmpw $disksizes+4, %si + jae got_sectors /* if all else fails, try 9 */ + xchgw %cx,%ax /* cx = track and sector */ + xorw %dx,%dx /* drive 0, head 0 */ + movw $0x0200, %bx /* address after boot sector */ + /* (512 bytes from origin, es = cs) */ + movw $0x0201, %ax /* service 2, 1 sector */ + int $0x13 + jc probe_loop /* try next value */ + +got_sectors: + movw $msg1end-msg1, %cx + movw $msg1, %si + call print_str + +/* ok, we've written the Loading... message, now we want to load the system */ + + movw $SYSSEG, %ax + movw %ax,%es /* segment of SYSSEG<<4 */ + pushw %es + call read_it + +/* This turns off the floppy drive motor, so that we enter the kernel in a + * known state, and don't have to worry about it later. + */ + movw $0x3f2, %dx + xorb %al,%al + outb %al,%dx + + call print_nl + pop %es /* = SYSSEG */ + +/* Restore original disk parameters */ + movw $0x78, %bx + movw dpoff, %di + movw dpseg, %si + xorw %ax,%ax + movw %ax,%ds + movw %di,(%bx) + movw %si,2(%bx) + + /* Everything now loaded. %es = SYSSEG, so %es:0000 points to + * start of loaded image. + */ + + /* Jump to loaded copy */ + ljmp $SYSSEG, $start_runtime + +endseg: .word SYSSEG + .section ".zinfo.fixup", "a", @progbits /* Compressor fixups */ + .ascii "ADDW" + .long endseg + .long 16 + .long 0 + .previous + +/* This routine loads the system at address SYSSEG<<4, making sure no 64kB + * boundaries are crossed. We try to load it as fast as possible, loading whole + * tracks whenever we can. + * + * in: es - starting address segment (normally SYSSEG) + */ +read_it: + movw $0,sread /* load whole image including prefix */ + movw %es,%ax + testw $0x0fff, %ax +die: jne die /* es must be at 64kB boundary */ + xorw %bx,%bx /* bx is starting address within segment */ +rp_read: + movw %es,%ax + movw %bx,%dx + movb $4, %cl + shrw %cl,%dx /* bx is always divisible by 16 */ + addw %dx,%ax + cmpw endseg, %ax /* have we loaded all yet? */ + jb ok1_read + ret +ok1_read: + movw sectors, %ax + subw sread, %ax + movw %ax,%cx + shlw $9, %cx + addw %bx,%cx + jnc ok2_read + je ok2_read + xorw %ax,%ax + subw %bx,%ax + shrw $9, %ax +ok2_read: + call read_track + movw %ax,%cx + addw sread, %ax + cmpw sectors, %ax + jne ok3_read + movw $1, %ax + subw head, %ax + jne ok4_read + incw track +ok4_read: + movw %ax, head + xorw %ax,%ax +ok3_read: + movw %ax, sread + shlw $9, %cx + addw %cx,%bx + jnc rp_read + movw %es,%ax + addb $0x10, %ah + movw %ax,%es + xorw %bx,%bx + jmp rp_read + +read_track: + pusha + pushw %ax + pushw %bx + pushw %bp /* just in case the BIOS is buggy */ + movw $0x0e2e, %ax /* 0x2e = . */ + movw $0x0007, %bx + int $0x10 + popw %bp + popw %bx + popw %ax + + movw track, %dx + movw sread, %cx + incw %cx + movb %dl,%ch + movw head, %dx + movb %dl,%dh + andw $0x0100, %dx + movb $2, %ah + + pushw %dx /* save for error dump */ + pushw %cx + pushw %bx + pushw %ax + + int $0x13 + jc bad_rt + addw $8, %sp + popa + ret + +bad_rt: pushw %ax /* save error code */ + call print_all /* ah = error, al = read */ + + xorb %ah,%ah + xorb %dl,%dl + int $0x13 + + addw $10, %sp + popa + jmp read_track + +/* print_all is for debugging purposes. It will print out all of the registers. + * The assumption is that this is called from a routine, with a stack frame like + * dx + * cx + * bx + * ax + * error + * ret <- sp + */ + +print_all: + call print_nl /* nl for readability */ + movw $5, %cx /* error code + 4 registers */ + movw %sp,%bp + +print_loop: + pushw %cx /* save count left */ + + cmpb $5, %cl + jae no_reg /* see if register name is needed */ + + movw $0x0007, %bx /* page 0, attribute 7 (normal) */ + movw $0xe05+0x41-1, %ax + subb %cl,%al + int $0x10 + + movb $0x58, %al /* 'X' */ + int $0x10 + + movb $0x3A, %al /* ':' */ + int $0x10 + +no_reg: + addw $2, %bp /* next register */ + call print_hex /* print it */ + movb $0x20, %al /* print a space */ + int $0x10 + popw %cx + loop print_loop + call print_nl /* nl for readability */ + ret + +print_str: + movw $0x0007, %bx /* page 0, attribute 7 (normal) */ + movb $0x0e, %ah /* write char, tty mode */ +prloop: + lodsb + int $0x10 + loop prloop + ret + +print_nl: + movw $0x0007, %bx /* page 0, attribute 7 (normal) */ + movw $0xe0d, %ax /* CR */ + int $0x10 + movb $0xa, %al /* LF */ + int $0x10 + ret + +/* print_hex prints the word pointed to by ss:bp in hexadecimal. */ + +print_hex: + movw (%bp),%dx /* load word into dx */ + movb $4, %cl + movb $0x0e, %ah /* write char, tty mode */ + movw $0x0007, %bx /* page 0, attribute 7 (normal) */ + call print_digit + call print_digit + call print_digit +/* fall through */ +print_digit: + rol %cl,%dx /* rotate so that lowest 4 bits are used */ + movb $0x0f, %al /* mask for nybble */ + andb %dl,%al + addb $0x90, %al /* convert al to ascii hex (four instructions) */ + daa + adcb $0x40, %al + daa + int $0x10 + ret + +sread: .word 0 /* sectors read of current track */ +head: .word 0 /* current head */ +track: .word 0 /* current track */ + +sectors: + .word 0 + +dpseg: .word 0 +dpoff: .word 0 + +disksizes: + .byte 36,18,15,9 + +msg1: + .ascii "Loading ROM image" +msg1end: + + .org 510, 0 + .word 0xAA55 + +start_runtime: + /* Install gPXE */ + call install + + /* Set up real-mode stack */ + movw %bx, %ss + movw $_estack16, %sp + + /* Jump to .text16 segment */ + pushw %ax + pushw $1f + lret + .section ".text16", "awx", @progbits +1: + pushl $main + pushw %cs + call prot_call + popl %ecx /* discard */ + + /* Uninstall gPXE */ + call uninstall + + /* Boot next device */ + int $0x18 + |