DCPU BOOTING SPECIFICATION V0.1
by SecretReaction (from /r/0x10c and /r/dcpu16)

1. Introduction

This document specifies the bootloader mechanism for the DCPU and it's associated hardware.

This document is a working specification, it may be changed or updated over time. It currently has not received any community input, and thus is likely going to have changes or updates in the near future.

The contents of this document are based on specifications that are not final, and thus this document may no longer be valid if they have a major change.

2. Machine State

a. Registers
{A, B, C, X, Y, EX, SP, IA, PC} = 0
Z = Device booted from.
{I, J} = Dependent on the type of device booted from.

b. Memory
Bootloader code will be loaded to memory address 0. Additional data may be loaded immediately after the bootloader in memory, depending on the type of device being booted from.

c. Hardware
All hardware will not be mapped to memory, nor will they send interrupt signals, nor will they be busy in any sort of way.

3. Boot Code

The only requirement for the bootloader code is that the last word must equal 0x10AD on some devices.

If this signature is required, and is lacking, the device will not be considered bootable, and will be passed on for other devices.

4. Booting from Disk Device

Registers I and J are equal to 0 when loading from a disk device.

The bootloader is loaded from the first sector of the disk. No additional data will be loaded into memory.

The bootloader must include the boot signature.

5. Booting from Other Hardware

This specification is specifically left vague in terms of booting from other devices. As more device specifications are added, this document will be updated with their boot processes.