Build Instructions.txt

MSDOS 2.11 adapted for the Just for Fun v20mbc
Requires 512KB

![My Image](pic.PNG)

Hardware and firmware:
https://j4f.info/v20-mbc

Set up for building on win32, can build on other platforms
Just need an assembler. 

Buildable MSDOS source obtained from pcjs
https://www.pcjs.org/blog/2018/11/21/

Derived from MS repo
https://github.com/microsoft/MS-DOS


You will need dosbox-x
https://dosbox-x.com/

Win32 nasm is included. Use a nasm for your platform. 

build loader with nasm: nasm loader.asm -fbin

copy loader.asm autoboot.bin

Edit skelio.asm to your tastes, primarily to set max memory size - 
	bios size in paragraphs is used to calculate location of msdos.sys
	A paragraph is 16 bytes.
	since loader loads logical sectors, this is the position of msdos in memory
	The fat12 format used is 8 sectors/cluster. 
	msdos will be 512*8 bytes after start of bios
	If your bios becomes larger than 4kb, this will be 512*16
	You may need to alter the loader. 

	Bios size - this allows moving msdos.sys to just after the 
	bios to save some bytes of memory. I am currently wasting 
	space

	Bios segment - this is where the loader places the bios, 
			my loader uses 00C0

	There is only one drive. Attempting to scan may cause problems
	Pay attention to root directory size

	If you change the boot block definition, you will need
	to alter seltrack to account for a different sectors per track
	The value is hard coded. 

Run dosbox-x with the build-msdos.cfg

Run dosbox-x with the build-image.cfg
This is not automatic. Watch for errors

***AT PROMPT SEGMENT NEEDED ENTER YOUR BIOS SEGMENT (00C0)***
 
copy autoboot.bin and ds00n00.dsk & ds01n00.dsk to v20mbc 	

Adding software - 
	mount the disk image in dosbox-x
	imgmount f ds1n00.dsk -t hdd -fs fat

	You can now copy files to the image. Close dosbox-x
	and recopy.