| 1 | #if defined (BIOS) |
| 2 | |
| 3 | #include <stdint.h> |
| 4 | #include <stddef.h> |
| 5 | #include <stdbool.h> |
| 6 | #include <sys/a20.h> |
| 7 | #include <sys/cpu.h> |
| 8 | #include <lib/real.h> |
| 9 | |
| 10 | #define A20_KBC_TIMEOUT 50000 |
| 11 | |
| 12 | static bool a20_kbc_wait(uint8_t mask, uint8_t expected) { |
| 13 | for (int i = 0; i < A20_KBC_TIMEOUT; i++) { |
| 14 | if ((inb(0x64) & mask) == expected) |
| 15 | return true; |
| 16 | } |
| 17 | return false; |
| 18 | } |
| 19 | |
| 20 | bool a20_check(void) { |
| 21 | bool ret = false; |
| 22 | uint16_t orig = mminw(0x7dfe); |
| 23 | |
| 24 | mmoutw(0x7dfe, 0x1234); |
| 25 | |
| 26 | if (mminw(0x7dfe) != mminw(0x7dfe + 0x100000)) { |
| 27 | ret = true; |
| 28 | goto out; |
| 29 | } |
| 30 | |
| 31 | mmoutw(0x7dfe, ~mminw(0x7dfe)); |
| 32 | |
| 33 | if (mminw(0x7dfe) != mminw(0x7dfe + 0x100000)) { |
| 34 | ret = true; |
| 35 | goto out; |
| 36 | } |
| 37 | |
| 38 | out: |
| 39 | mmoutw(0x7dfe, orig); |
| 40 | return ret; |
| 41 | } |
| 42 | |
| 43 | // Keyboard controller method code below taken from: |
| 44 | // https://wiki.osdev.org/A20_Line |
| 45 | |
| 46 | bool a20_enable(void) { |
| 47 | if (a20_check()) |
| 48 | return true; |
| 49 | |
| 50 | // BIOS method |
| 51 | struct rm_regs r = {0}; |
| 52 | r.eax = 0x2401; |
| 53 | rm_int(0x15, &r, &r); |
| 54 | |
| 55 | if (a20_check()) |
| 56 | return true; |
| 57 | |
| 58 | // Keyboard controller method (with timeout for systems without KBC) |
| 59 | if (!a20_kbc_wait(2, 0)) goto kbc_failed; |
| 60 | outb(0x64, 0xad); |
| 61 | if (!a20_kbc_wait(2, 0)) goto kbc_failed; |
| 62 | outb(0x64, 0xd0); |
| 63 | if (!a20_kbc_wait(1, 1)) goto kbc_failed; |
| 64 | uint8_t b = inb(0x60); |
| 65 | if (!a20_kbc_wait(2, 0)) goto kbc_failed; |
| 66 | outb(0x64, 0xd1); |
| 67 | if (!a20_kbc_wait(2, 0)) goto kbc_failed; |
| 68 | outb(0x60, b | 2); |
| 69 | if (!a20_kbc_wait(2, 0)) goto kbc_failed; |
| 70 | outb(0x64, 0xae); |
| 71 | if (!a20_kbc_wait(2, 0)) goto kbc_failed; |
| 72 | |
| 73 | if (a20_check()) |
| 74 | return true; |
| 75 | |
| 76 | kbc_failed: |
| 77 | |
| 78 | // Fast A20 method |
| 79 | b = inb(0x92); |
| 80 | if ((b & 0x02) == 0) { |
| 81 | b &= ~0x01; |
| 82 | b |= 0x02; |
| 83 | outb(0x92, b); |
| 84 | } |
| 85 | |
| 86 | if (a20_check()) |
| 87 | return true; |
| 88 | |
| 89 | return false; |
| 90 | } |
| 91 | |
| 92 | #endif |
