ref: 205f12720ed76a86a1eb01f756ef9a7099943fb4
dir: /sys/src/boot/pc/a20.s/
#include "x16.h" #undef ORB TEXT a20(SB), $0 CALL rmode16(SB) STI LWI(0x2401, rAX) BIOSCALL(0x15) JC _biosfail CALL16(pmode32(SB)) RET _biosfail: CALL16(pmode32(SB)) /* fast a20 */ MOVL $0x92, DX INB ANDB $0xFE, AX ORB $0x02, AX OUTB /* slow a20 */ CALL a20wait(SB) MOVL $0x64, DX MOVB $0xAD, AL OUTB CALL a20wait(SB) MOVL $0x64, DX MOVB $0xD0, AL OUTB CALL a20wait2(SB) MOVL $0x60, DX INB PUSHL AX CALL a20wait(SB) MOVL $0x64, DX MOVB $0xD1, AL OUTB CALL a20wait(SB) MOVL $0x60, DX POPL AX ORB $2, AL OUTB CALL a20wait(SB) MOVL $0x64, DX MOVB $0xAE, AL OUTB TEXT a20wait(SB), $0 _a20wait: MOVL $0x64, DX INB TESTB $1, AL JZ _a20wait2 RET TEXT a20wait2(SB), $0 _a20wait2: MOVL $0x64, DX INB TESTB $2, AL JNZ _a20wait RET