81 lines
1.4 KiB
C
81 lines
1.4 KiB
C
#if defined (BIOS)
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#include <stdint.h>
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#include <stddef.h>
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#include <stdbool.h>
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#include <sys/a20.h>
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#include <sys/cpu.h>
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#include <lib/real.h>
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bool a20_check(void) {
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bool ret = false;
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uint16_t orig = mminw(0x7dfe);
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mmoutw(0x7dfe, 0x1234);
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if (mminw(0x7dfe) != mminw(0x7dfe + 0x100000)) {
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ret = true;
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goto out;
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}
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mmoutw(0x7dfe, ~mminw(0x7dfe));
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if (mminw(0x7dfe) != mminw(0x7dfe + 0x100000)) {
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ret = true;
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goto out;
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}
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out:
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mmoutw(0x7dfe, orig);
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return ret;
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}
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// Keyboard controller method code below taken from:
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// https://wiki.osdev.org/A20_Line
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bool a20_enable(void) {
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if (a20_check())
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return true;
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// BIOS method
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struct rm_regs r = {0};
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r.eax = 0x2401;
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rm_int(0x15, &r, &r);
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if (a20_check())
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return true;
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// Keyboard controller method
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while (inb(0x64) & 2);
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outb(0x64, 0xad);
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while (inb(0x64) & 2);
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outb(0x64, 0xd0);
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while (!(inb(0x64) & 1));
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uint8_t b = inb(0x60);
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while (inb(0x64) & 2);
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outb(0x64, 0xd1);
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while (inb(0x64) & 2);
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outb(0x60, b | 2);
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while (inb(0x64) & 2);
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outb(0x64, 0xae);
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while (inb(0x64) & 2);
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if (a20_check())
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return true;
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// Fast A20 method
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b = inb(0x92);
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if ((b & 0x02) == 0) {
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b &= ~0x01;
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b |= 0x02;
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outb(0x92, b);
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}
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if (a20_check())
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return true;
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return false;
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}
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#endif
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