Got rid of vga_print in assembly
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e75bf391ee
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512f348d74
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@ -90,11 +90,7 @@ load_kernel:
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[bits 32]
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BEGIN_32BIT: ; After the switch we will get here
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mov esi, protected_mode_msg
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call vga_print
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call enableA20
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mov esi, calling_kernel_msg
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call vga_print
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call kernel_offset
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cli
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hlt
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@ -109,9 +105,7 @@ BEGIN_32BIT: ; After the switch we will get here
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; Here we define our variables used in the second stage
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protected_mode_msg: db "TSBL - INFO: Successfully switched to protected mode, enabling A20 line", 0
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kernel_loaded_msg: db "TSBL - INFO: Kernel loaded, switching to protected mode", 0
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calling_kernel_msg: db "TSBL - INFO: Calling kernel entrypoint", 0
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stage2_loaded_msg: db "TSBL - INFO: Stage 2 loaded, loading kernel", 0
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@ -58,5 +58,5 @@ disk_loop:
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parenthesis: db ')', 0
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disk_read_error_msg: db "TSOS - ERROR: Disk read failed (error code ", 0
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disk_sectors_error_msg: db "TSOS - ERROR: Disk read failed (sector number mismatch)", 0
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disk_read_error_msg: db "TSBL - ERROR: Disk read failed (error code ", 0
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disk_sectors_error_msg: db "TSBL - ERROR: Disk read failed (sector number mismatch)", 0
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@ -182,11 +182,7 @@ enableA20:
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;; Here you may or may not want to print a warning message about
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;; the fact that we had to use the nonstandard alternate enabling
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;; method
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mov esi, a20_warning_msg
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call vga_print
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.success:
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mov esi, a20_enabled_msg
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call vga_print
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;sti ; Note: When this is uncommented, shit breaks. I have a few theories as to why,
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; but none of them make sense, so ¯\_(ツ)_/¯
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@ -199,8 +195,3 @@ enableA20:
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popa
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mov eax, -1
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ret
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a20_enabled_msg: db "TSBL - INFO: A20 line enabled successfully", 0
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a20_warning_msg: db "TSBL - WARN: A20 line was enabled with nonstandard method", 0
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a20_failed_msg: db "TSBL - ERROR: Failed to enable A20 line"
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@ -121,83 +121,3 @@ bios_cls:
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HEX_OUT: db '0x0000', 0 ; reserve memory for our new string
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[bits 32]
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; I/O routines that work with the VGA controller and video memory
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; to print to the screen
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VMEM_START: equ 0xb8000 ; Video memory always starts at this address
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; A character on the screen in VGA text mode is composed of 2 bytes:
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; the first byte is the ASCII codepoint to be printed, while the next
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; octet represents additional formatting information (color, blink,
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; underline, etc.). More info: https://en.wikipedia.org/wiki/VGA_text_mode
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TEXT_COLOR: equ 0x07
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vga_print:
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; Prints a null-terminated string located
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; on the esi register.
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pusha
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mov ebx, VMEM_START
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vga_print_loop:
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mov al, [esi]
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cmp al, 0
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je vga_print_done
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mov ah, TEXT_COLOR
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mov [ebx], ax ; Write the 2-byte character to video memory
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inc esi ; Go to the next character in the string
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add ebx, 2
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jmp vga_print_loop
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vga_print_done:
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popa
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ret
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vga_printh:
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; Prints the value of edx in hexadecimal format
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pusha
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xor ecx, ecx ; This serves as our index and loop counter
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vga_printh_loop:
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cmp ecx, 8 ; loop 8 times
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je vga_printh_end
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; Here we extract the last digit from edx using
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; a bitmask, with eax as our working register,
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; and convert it to ASCII by adding 30 to it if
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; it's less than 9 (meaning it's a digit) or 37
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; if if it's a letter (that's because letters and
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; numbers are 7 digits apart in the ASCII table)
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mov eax, edx
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and eax, 0xf
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add ax, 0x30
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cmp ax, 0x39
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jle vga_printh_step2
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add ax, 7
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vga_printh_step2:
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; Now we start filling our string variable (starting from the
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; back, since we are extracting digits from the end of the
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; number) and then rotate the number by 4 bits to access the
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; next digit. This works and is the same as the more common
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; modulo division because each hexadecimal digits represents
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; exactly 4 bits and we can take advantage of the CPU's much
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; faster bitwise operations rather than burden ourselves with
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; a costly modulo 10 division (which would take hundreds of
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; clock cycles, as opposed to it only taking one for a rotate
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; operation)
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mov esi, HEX_OUT_LONG + 9 ; We skip the '0x' part and jump to the last digit
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sub esi, ecx ; We subtract esi by ecx so we land on the right digit
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mov [esi], ax ; We copy the character in ax to the character pointed to by esi
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ror edx, 4 ; With an example input: 0x1234 -> 0x4123 -> 0x3412 -> 0x2341 -> 0x1234
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inc ecx
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jmp vga_printh_loop
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vga_printh_end:
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mov esi, HEX_OUT_LONG
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call vga_print
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popa
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ret
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HEX_OUT_LONG: db '0x00000000', 0
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