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Unshave four bytes for IBM PC compatibility

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Ability to run on original hardware is confirmed.
This commit is contained in:
Justine Tunney 2021-11-16 10:45:40 -08:00
parent 1e9c7fca35
commit e90a728894
1 changed files with 5 additions and 9 deletions
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14
sectorlisp.S
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@ -20,6 +20,7 @@
╚─────────────────────────────────────────────────────────────────────────────*/
// LISP meta-circular evaluator in a MBR
// Compatible with the original hardware
.set ATOM_NIL, (kNil-kSymbols)<<1|1
.set ATOM_QUOTE, (kQuote-kSymbols)<<1|1
@ -38,11 +39,6 @@
.set ONE, %cx
.set TWO, %bx
////////////////////////////////////////////////////////////////////////////////
// Currently requires i386+ in real mode
// Can be easily tuned for the IBM PC XT
// Quoth xed -r -isa-set -i sectorlisp.o
.section .text,"ax",@progbits
.type kSymbols,@object
.type _begin,@function
@ -73,10 +69,10 @@ _begin: push %cs # memory model ds=es=ss=cs
cld # clear direction flag
rep stosb # memset(0x8000,0,0x8000)
push %ds # cx is now zero
# cli # disable interrupts
cli # disable interrupts
pop %ss # disable nonmaskable interrupts
mov %ax,%sp # use null pointer as our stack
# sti # enable interrupts
sti # enable interrupts
inc ONE # ++cx
mov ONE,TWO
inc TWO
@ -181,10 +177,10 @@ GetChar:
# ah is bios scancode
# al is ascii character
PutChar:
# push %bp # original ibm pc scroll up bug
push %bp # original ibm pc scroll up bug
mov $0x0e,%ah # teletype output al cp437
int $0x10 # vidya service
# pop %bp # preserves al
pop %bp # preserves al
cmp $'\r',%al # don't clobber stuff
jne .ret
mov $'\n',%al