initial commit with some old assembly stuff

6 files changed, 107 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3d4322a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+print
+printb
+boot.img
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..c9438a6
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,12 @@
+boot.img: print printb
+	cat print printb > boot.img
+
+print: print.asm
+	nasm -Wall print.asm
+
+printb: printb.asm
+	nasm -Wall printb.asm
+
+.PHONY: run
+run: boot.img
+	qemu-system-i386 -drive file=boot.img,format=raw,index=0,if=floppy
diff --git a/README.adoc b/README.adoc
new file mode 100644
index 0000000..9ee985a
--- /dev/null
+++ b/README.adoc
@@ -0,0 +1,4 @@
+== Assembly Stuff
+
+Trying to do some low-level i386 assembly. I apparently succeeded loading some
+data from a virtual floppy disk. Maybe, one day, I'll try to do more.
diff --git a/TODO b/TODO
new file mode 100644
index 0000000..34dec0a
--- /dev/null
+++ b/TODO
@@ -0,0 +1,8 @@
+* boot loader, loading a few sectors into memory
+* output from loadable
+* setting up things to transition to protected mode
+  * defining a software interrupt in order to call a print() function
+* setting up things to transition to long mode
+  * defining a syscall on order to call a print() function
+* writing minimal program in C
+* writing a minimal scheduler and running two programs at the same time
diff --git a/print.asm b/print.asm
new file mode 100644
index 0000000..97acd8b
--- /dev/null
+++ b/print.asm
@@ -0,0 +1,44 @@
+org 7C00h
+
+jmp _start
+
+hello: db 'Hello from the first stage!', 0x0A, 0x0D, 0x0
+
+_start:
+
+; print hello message
+
+mov ah, 0x0E
+xor esi, esi
+xor edi, edi
+mov si, hello
+cld
+
+.loop:
+lodsb
+cmp al, 0x00
+je .out
+int 0x10
+jmp .loop
+.out:
+
+; load sectors from disk and jump there
+
+mov ah, 0x02 ; load sectory from disk
+mov al, 0x01 ; load one sector
+xor ch, ch   ; cylinder number
+mov cl, 0x02 ; start from sector 2
+xor dh, dh   ; head number
+xor dl, dl   ; drive number
+
+mov bx, 0x0500 ; start address (see jmp)
+               ; 0x00000500 to 0x00007BFF, from Overview at http://wiki.osdev.org/Memory_Map_%28x86%29
+int 0x13
+
+jmp 0x0500
+
+jmp $
+
+; stolen from: https://en.wikibooks.org/wiki/X86_Assembly/Bootloaders
+times 0200h - 2 - ($ - $$)  db 0    ;Zerofill up to 510 bytes
+dw 0AA55h       ;Boot Sector signature
diff --git a/printb.asm b/printb.asm
new file mode 100644
index 0000000..a8fa788
--- /dev/null
+++ b/printb.asm
@@ -0,0 +1,36 @@
+org 0x0500
+
+
+SECTION .data
+boot: db 'Welcome to the second stage!', 0x0A, 0x0D, 0x00
+foo: db 'What a nice message this is!', 0x0A, 0x0D, 0x00
+
+SECTION .text
+
+
+jmp start
+
+print:
+	push ax
+	cld
+	mov ah, 0x0E
+
+	.loop:
+	lodsb
+	cmp al, 0x00
+	je .out
+	int 0x10
+	jmp .loop
+	.out:
+	pop ax
+	ret
+
+start:
+	mov si, boot
+	call print
+
+	mov si, foo
+	call print
+
+; maybe to something here...
+; e.g.: how to keep CPU from spinning at 100%