sys: parse drive number and load BPB

Makefile

@@ -11,7 +11,7 @@ PRODUCT = rdos
 LABEL = $(PRODUCT) $(VERSION)
 
 NASM = nasm
-NASM_ARGS = -s -Ilib -DPRODUCT=$(PRODUCT) -DVERSION=$(VERSION)
+NASM_ARGS = -s -Ilib --before "cpu 8086" -DPRODUCT=$(PRODUCT) -DVERSION=$(VERSION)
 
 QEMU_ARGS += $(shell test -w /dev/kvm && echo --enable-kvm)
 
@@ -28,7 +28,7 @@ SYS = host/sys.elf
 FIXROM = host/fix-rom.elf
 
 .PHONY: default clean qemu-floppy5 qemu-floppy3
-.PRECIOUS: $(DISTFILES)
+.PRECIOUS: %.com
 
 default: fd1440.img
 
@@ -37,7 +37,7 @@ host/%.elf: host/%.c
 	$(CC) -o $@ $<
 
 # COM programs
-%.com: com/%.asm
+%.com: src/%.asm src/*.inc
 	$(NASM) $(NASM_ARGS) -o $@ $<
 
 # Bootloaders, first sector on partition
@@ -86,5 +86,8 @@ qemu-hdd: hdd.img $(ROMS)
 qemu-uartctrl: uartctrl.rom chartab.bs
 	$(QEMU) $(QEMU_ARGS) -option-rom uartctrl.rom -serial stdio -hda chartab.bs
 
-dosbox-%: %.com
-	dosbox -c "mount P $(CURDIR)" -c "P:" -c "$< $(ARGS)"
+dosbox-%: %.com fd1440.img
+	dosbox -c "mount P $(CURDIR)" -c "P:" -c "IMGMOUNT A: FD1440.IMG -t floppy" -c "$< $(ARGS)" -c "pause" -c "exit"
+
+emu2-%: %.com
+	emu2 $< $(ARGS)