hammer/kernel.asm at main · Semuca/hammer · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
BITS 32

VGA_WIDTH equ 80
VGA_HEIGHT equ 25

VGA_COLOR_BLACK equ 0
VGA_COLOR_BLUE equ 1
VGA_COLOR_GREEN equ 2
VGA_COLOR_CYAN equ 3
VGA_COLOR_RED equ 4
VGA_COLOR_MAGENTA equ 5
VGA_COLOR_BROWN equ 6
VGA_COLOR_LIGHT_GREY equ 7
VGA_COLOR_DARK_GREY equ 8
VGA_COLOR_LIGHT_BLUE equ 9
VGA_COLOR_LIGHT_GREEN equ 10
VGA_COLOR_LIGHT_CYAN equ 11
VGA_COLOR_LIGHT_RED equ 12
VGA_COLOR_LIGHT_MAGENTA equ 13
VGA_COLOR_LIGHT_BROWN equ 14
VGA_COLOR_WHITE equ 15

global kernel_main
kernel_main:
    mov dh, VGA_COLOR_LIGHT_GREY
    mov dl, VGA_COLOR_BLACK
    call terminal_set_color
    mov esi, hello_string
    call terminal_write_string
    jmp $


; IN = dl: y, dh: x
; OUT = dx: Index with offset 0xB8000 at VGA buffer
; Other registers preserved
terminal_getidx:
    push ax; preserve registers

    shl dh, 1 ; multiply by two because every entry is a word that takes up 2 bytes

    mov al, VGA_WIDTH
    mul dl
    mov dl, al

    shl dl, 1 ; same
    add dl, dh
    mov dh, 0

    pop ax
    ret

; IN = dl: bg color, dh: fg color
; OUT = none
terminal_set_color:
    shl dl, 4

    or dl, dh
    mov [terminal_color], dl


    ret

; IN = dl: y, dh: x, al: ASCII char
; OUT = none
terminal_putentryat:
    pusha
    call terminal_getidx
    mov ebx, edx

    mov dl, [terminal_color]
    mov byte [0xB8000 + ebx], al
    mov byte [0xB8001 + ebx], dl


    popa
    ret

; IN = al: ASCII char
terminal_putchar:
    mov dx, [terminal_cursor_pos] ; This loads terminal_column at DH, and terminal_row at DL

    call terminal_putentryat

    inc dh
    cmp dh, VGA_WIDTH
    jne .cursor_moved

    mov dh, 0
    inc dl

    cmp dl, VGA_HEIGHT
    jne .cursor_moved

    mov dl, 0


.cursor_moved:
    ; Store new cursor position
    mov [terminal_cursor_pos], dx

    ret

; IN = cx: length of string, ESI: string location
; OUT = none
terminal_write:
    pusha
.loopy:

    mov al, [esi]
    call terminal_putchar

    dec cx
    cmp cx, 0
    je .done

    inc esi
    jmp .loopy


.done:
    popa
    ret

; IN = ESI: zero delimited string location
; OUT = ECX: length of string
terminal_strlen:
    push eax
    push esi
    mov ecx, 0
.loopy:
    mov al, [esi]
    cmp al, 0
    je .done

    inc esi
    inc ecx

    jmp .loopy


.done:
    pop esi
    pop eax
    ret

; IN = ESI: string location
; OUT = none
terminal_write_string:
    pusha
    call terminal_strlen
    call terminal_write
    popa
    ret

; Exercises:
; - Newline support
; - Terminal scrolling when screen is full
; Note:
; - The string is looped through twice on printing.

hello_string db "Hello, kernel World!", 0xA, 0 ; 0xA = line feed


terminal_color db 0

terminal_cursor_pos:
terminal_column db 0
terminal_row db 0