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collapseos/blk/811
Virgil Dupras 1a467efae1 pcat: use a far jump to boot into the OS
Unless I misunderstood, this is supposed to set CS. This would make
all SREG have the same value. This allows us to remove BIN( offset
from os.bin.

I've tried booting to offset 0, but it didn't seem to work. Let's
settle for 0x8000. 512kb of system RAM is way more than we need
anyways.
2020-06-13 20:06:51 -04:00

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H@ ORG ! 0x7c00 BIN( ! ( BIOS loads boot bin at 0x7c00 )
JMPs, L1 FWRs ( start )
ORG @ 0x25 + HERE ! ( bypass BPB )
L1 FSET ( start )
CLI, CLD, AX 0x800 MOVxi, DS AX MOVsx, ES AX MOVsx,
SS AX MOVsx, SP 0xffff MOVxi, STI,
AH 2 MOVri, DX 0 MOVxi, CH 0 MOVri, CL 2 MOVri, AL 1 MOVri,
BX 0 MOVxi, 0x13 INT, ( read 2nd sector of boot floppy )
0x800 0 JMPf,
ORG @ 0x1fe + HERE ! 0x55 A, 0xaa A,