Got rid of vga_print in assembly

This commit is contained in:
Mattia Giambirtone 2022-11-19 11:02:51 +01:00
parent e75bf391ee
commit 512f348d74
4 changed files with 2 additions and 97 deletions

View File

@ -90,11 +90,7 @@ load_kernel:
[bits 32]
BEGIN_32BIT: ; After the switch we will get here
mov esi, protected_mode_msg
call vga_print
call enableA20
mov esi, calling_kernel_msg
call vga_print
call kernel_offset
cli
hlt
@ -109,9 +105,7 @@ BEGIN_32BIT: ; After the switch we will get here
; Here we define our variables used in the second stage
protected_mode_msg: db "TSBL - INFO: Successfully switched to protected mode, enabling A20 line", 0
kernel_loaded_msg: db "TSBL - INFO: Kernel loaded, switching to protected mode", 0
calling_kernel_msg: db "TSBL - INFO: Calling kernel entrypoint", 0
stage2_loaded_msg: db "TSBL - INFO: Stage 2 loaded, loading kernel", 0

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@ -58,5 +58,5 @@ disk_loop:
parenthesis: db ')', 0
disk_read_error_msg: db "TSOS - ERROR: Disk read failed (error code ", 0
disk_sectors_error_msg: db "TSOS - ERROR: Disk read failed (sector number mismatch)", 0
disk_read_error_msg: db "TSBL - ERROR: Disk read failed (error code ", 0
disk_sectors_error_msg: db "TSBL - ERROR: Disk read failed (sector number mismatch)", 0

View File

@ -182,11 +182,7 @@ enableA20:
;; Here you may or may not want to print a warning message about
;; the fact that we had to use the nonstandard alternate enabling
;; method
mov esi, a20_warning_msg
call vga_print
.success:
mov esi, a20_enabled_msg
call vga_print
;sti ; Note: When this is uncommented, shit breaks. I have a few theories as to why,
; but none of them make sense, so ¯\_(ツ)_/¯
@ -199,8 +195,3 @@ enableA20:
popa
mov eax, -1
ret
a20_enabled_msg: db "TSBL - INFO: A20 line enabled successfully", 0
a20_warning_msg: db "TSBL - WARN: A20 line was enabled with nonstandard method", 0
a20_failed_msg: db "TSBL - ERROR: Failed to enable A20 line"

View File

@ -121,83 +121,3 @@ bios_cls:
HEX_OUT: db '0x0000', 0 ; reserve memory for our new string
[bits 32]
; I/O routines that work with the VGA controller and video memory
; to print to the screen
VMEM_START: equ 0xb8000 ; Video memory always starts at this address
; A character on the screen in VGA text mode is composed of 2 bytes:
; the first byte is the ASCII codepoint to be printed, while the next
; octet represents additional formatting information (color, blink,
; underline, etc.). More info: https://en.wikipedia.org/wiki/VGA_text_mode
TEXT_COLOR: equ 0x07
vga_print:
; Prints a null-terminated string located
; on the esi register.
pusha
mov ebx, VMEM_START
vga_print_loop:
mov al, [esi]
cmp al, 0
je vga_print_done
mov ah, TEXT_COLOR
mov [ebx], ax ; Write the 2-byte character to video memory
inc esi ; Go to the next character in the string
add ebx, 2
jmp vga_print_loop
vga_print_done:
popa
ret
vga_printh:
; Prints the value of edx in hexadecimal format
pusha
xor ecx, ecx ; This serves as our index and loop counter
vga_printh_loop:
cmp ecx, 8 ; loop 8 times
je vga_printh_end
; Here we extract the last digit from edx using
; a bitmask, with eax as our working register,
; and convert it to ASCII by adding 30 to it if
; it's less than 9 (meaning it's a digit) or 37
; if if it's a letter (that's because letters and
; numbers are 7 digits apart in the ASCII table)
mov eax, edx
and eax, 0xf
add ax, 0x30
cmp ax, 0x39
jle vga_printh_step2
add ax, 7
vga_printh_step2:
; Now we start filling our string variable (starting from the
; back, since we are extracting digits from the end of the
; number) and then rotate the number by 4 bits to access the
; next digit. This works and is the same as the more common
; modulo division because each hexadecimal digits represents
; exactly 4 bits and we can take advantage of the CPU's much
; faster bitwise operations rather than burden ourselves with
; a costly modulo 10 division (which would take hundreds of
; clock cycles, as opposed to it only taking one for a rotate
; operation)
mov esi, HEX_OUT_LONG + 9 ; We skip the '0x' part and jump to the last digit
sub esi, ecx ; We subtract esi by ecx so we land on the right digit
mov [esi], ax ; We copy the character in ax to the character pointed to by esi
ror edx, 4 ; With an example input: 0x1234 -> 0x4123 -> 0x3412 -> 0x2341 -> 0x1234
inc ecx
jmp vga_printh_loop
vga_printh_end:
mov esi, HEX_OUT_LONG
call vga_print
popa
ret
HEX_OUT_LONG: db '0x00000000', 0