From bd6235251321e8ba8f91121f7497dd778125d962 Mon Sep 17 00:00:00 2001
From: Robbe Van Herck <robbevanherck1@gmail.com>
Date: Fri, 27 Dec 2019 16:17:28 +0100
Subject: [PATCH] Reading and printing strings from hard drives

---
 .gitignore |   1 +
 Makefile   |   8 ++++
 drive.bin  | Bin 0 -> 33 bytes
 main.asm   | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 122 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 drive.bin
 create mode 100644 main.asm

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..97d14fb
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+boot.bin
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..a675331
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,8 @@
+compile_and_run: compile run
+
+compile:
+	rm -rf boot.bin
+	nasm -f bin -o boot.bin main.asm
+
+run:
+	qemu-system-x86_64 -drive format=raw,file=boot.bin -drive format=raw,file=drive.bin -monitor stdio
diff --git a/drive.bin b/drive.bin
new file mode 100644
index 0000000000000000000000000000000000000000..ade7f77b2f9b6af83ec28c2394d23a9c70ba570a
GIT binary patch
literal 33
ocmWH^$ShVUE-A{)OIJwF&rK~>NGr<ERme@v%`d7{u<~aB0MW$@y#N3J

literal 0
HcmV?d00001

diff --git a/main.asm b/main.asm
new file mode 100644
index 0000000..4986a18
--- /dev/null
+++ b/main.asm
@@ -0,0 +1,113 @@
+org 0x7C00                      
+bits 16                         
+
+jmp .start
+
+;;; Print string at bx
+.puts:
+.puts_loop:
+
+mov al, [bx]        ; load the character
+cmp al, 0           ; check for null byte
+je .end_puts_loop
+
+mov ah, 0x0e
+int 0x10            ; print charachter
+inc bx
+jmp .puts_loop
+.end_puts_loop:
+ret
+
+
+
+;;; Print bl as hex
+.puthex:
+
+; Print high bits
+mov dl, bl
+shr dl, 4
+
+cmp dl, 9
+jg .puthex_high_alpha
+
+; It's < 10, print as digit
+mov al, dl
+add al, 0x30
+mov ah, 0x0e
+int 0x10
+jmp .puthex_low
+
+.puthex_high_alpha:
+; It's >= 10, print as letter
+mov al, dl
+add al, 0x57 ; 0x57 = (0x61 - 10)
+mov ah, 0x0e
+int 0x10
+
+.puthex_low:
+; Print low bits
+mov dl, bl
+and dl, 0b1111
+
+cmp dl, 9
+jg .puthex_low_alpha
+
+; It's < 10, print as digit
+mov al, dl
+add al, 0x30
+mov ah, 0x0e
+int 0x10
+jmp .puthex_end
+
+.puthex_low_alpha:
+; It's >= 10, print as letter
+mov al, dl
+add al, 0x57 ; 0x57 = (0x61 - 10)
+mov ah, 0x0e
+int 0x10
+
+.puthex_end:
+ret
+
+
+
+.start:
+
+; reset disk system
+mov ah, 0x00
+mov dl, 0x81
+int 0x13
+
+; print result on error
+jnc .reset_disk_no_error
+mov bl, ah
+call .puthex
+.reset_disk_no_error:
+
+; Read sector 1 into memory
+mov ah, 0x02
+mov al, 0x01    ; number of sectors
+mov ch, 0x00    ; cylinder number, low 8 bits
+mov cl, 0x01    ; cylinder number, high 2 bits + sector number (6 bits)
+mov dh, 0x00    ; head number
+mov dl, 0x81    ; drive number
+mov bx, .data   ; data buffer
+int 0x13
+
+; print result on error
+jnc .read_disk_no_error
+mov bl, ah
+call .puthex
+.read_disk_no_error:
+
+; print string
+mov bx, .data
+call .puts
+
+.end:
+hlt
+
+.data:
+
+times 510 - ($ - $$) db 0
+dw 0xAA55
\ No newline at end of file