From 66289aa8ecfa07b20bad424eb9860b196641ef52 Mon Sep 17 00:00:00 2001
From: Brett Weiland <brett_weiland@bpcspace.com>
Date: Fri, 19 Mar 2021 10:54:25 -0500
Subject: first commit

---
 src/bootloader/bios_functions/bios_disk.asm | 38 +++++++++++++++++++
 src/bootloader/bios_functions/print.asm     | 59 +++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)
 create mode 100644 src/bootloader/bios_functions/bios_disk.asm
 create mode 100644 src/bootloader/bios_functions/print.asm

(limited to 'src/bootloader/bios_functions')

diff --git a/src/bootloader/bios_functions/bios_disk.asm b/src/bootloader/bios_functions/bios_disk.asm
new file mode 100644
index 0000000..28fc74d
--- /dev/null
+++ b/src/bootloader/bios_functions/bios_disk.asm
@@ -0,0 +1,38 @@
+bios_disk:
+.load_sectors:
+pusha
+mov es, dx
+
+mov ah, 0x02      ; read disc sectors
+mov ch, 0x00      ; track 0
+mov dh, 0x00      ; head 0
+mov dl, [stage0.boot_device]
+
+int 0x13
+
+jc .failed
+
+mov ah, 0
+popa
+ret
+
+.failed:
+
+mov bx, .loadsectors_error
+mov cx, 0
+call bios_print
+
+push 0
+mov al, ah
+mov ah, 0   ; you need to clean up the bios print function!
+push ax
+mov cx, 1
+mov bx, sp
+call bios_print
+
+
+mov ah, 1
+popa
+ret
+
+.loadsectors_error: db "Error loading sectors: ", 0
diff --git a/src/bootloader/bios_functions/print.asm b/src/bootloader/bios_functions/print.asm
new file mode 100644
index 0000000..d071cd9
--- /dev/null
+++ b/src/bootloader/bios_functions/print.asm
@@ -0,0 +1,59 @@
+;TODO fix null problem, allow direct passes
+bios_print:
+;push ax       ; we need to use ax, so let's push it in case whoever called needs it
+pusha
+mov ah, 0x0e  ; tells bios we're in tty mode
+
+.print_loop:
+mov al, [bx]          ; al is the char MEANT TO BE CX
+cmp al, 0             ; compare the char we're about to print with null
+je .fini   ; if it is null, we gonna scoot the fuck outta here
+
+test cx, cx           ; if cx is zero, ascii, otherwise hex string
+jne .print_hex
+int 0x10              ; bios call, actually prints the char
+.print_hex_ret:
+inc bx                ; adds to the pointer
+jmp .print_loop   ; goes back to loop start
+
+.fini:
+mov al, 0xd           ; \r
+int 0x10
+mov al, 0xa           ; \n
+int 0x10
+popa
+ret
+
+
+.print_hex:
+mov al, '0'
+int 0x10
+
+mov al, 'x'
+int 0x10
+
+mov al, [bx]              ; shift bits to get first nibble
+shr al, 4
+call .bios_print_nibble
+
+mov al, [bx]
+and al, 0x0f
+call .bios_print_nibble
+
+mov al, ' '
+int 0x10
+
+jmp .print_hex_ret
+
+
+.bios_print_nibble:
+cmp al, 9                 ; see if letter worthy
+ja .print_hex_letter
+add al, 0x30              ;'1'
+int 0x10
+ret
+
+.print_hex_letter:
+add al, 0x57              ;'a'
+int 0x10
+ret
-- 
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