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Improve detection of boot media on bare metal (#535)

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hello.com now starts up correctly on QEMU when run as a hard
disk image.
This commit is contained in:
tkchia 2022-08-14 23:32:58 +08:00 committed by GitHub
parent d36d0634db
commit 5584f6adcf
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1 changed files with 15 additions and 1 deletions
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16
ape/ape.S
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@ -301,7 +301,21 @@ pc: cld
// @since IBM Personal Computer XT // @since IBM Personal Computer XT
dsknfo: push %bx dsknfo: push %bx
1: push %dx 1: push %dx
mov $0x08,%ah # get disk params mov $0x16,%ah # make sure there is disk in drive,
int $0x13 # by querying change-line status
jnc 2f
xor %ax,%ax # if error or change line active,
int $0x13 # do a reset...
jc 9f
mov $0x0201,%ax # ...then do a read, to confirm that
mov $0x0001,%cx # there is disk in drive
mov $0,%dh # (verify (%ah = 4) does not work
mov $IMAGE_BASE_REAL>>4,%bx # under QEMU, which always returns
mov %bx,%es # success)
xor %bx,%bx
int $0x13
jc 9f
2: mov $0x08,%ah # get disk params
int $0x13 int $0x13
jc 9f jc 9f
mov %cl,%bh mov %cl,%bh