Skip to main content

Operating System

I've decided to write a small and very limited operating system called BluePrint-DOS (BP-DOS) for my computers, with the goal being to require a minimal amount of hardware, and to more easily facilitate running programs, by loading them from a block-storage device than burning an EEPROM every time a new program is to be tested/run.

The hardware requirements will be:

  • 32KB of RAM, to hold both OS routines and the running program
  • A free-running timer to facilitate CPU 'sleeping' when no action is being done.
  • A block storage device to store OS and program files.
  • User I/O, for hopefully obvious reasons.
The function of the OS itself will be to:
  • Load, run, and return from user programs.
  • Provide file system routines for reading/writing files to the selected block device.
Lower level functions will be stored in ROM, and these include:

  • Block-storage sector read/write routines.
  • User input hardware routines.
  • Timer interrupt service routine.
  • Display hardware routines.
  • Serial I/O routines. 

The OS itself will only be mono-tasking, and in fact will hand over all system control to the user program, only leaving behind useful hardware and filesystem routines. For any additional hardware, those will have to be driven by a user program. Upon exit, a user program will perform an additional RET instruction than there are CALL instructions in the user program, to return control to the OS.

As for the file system to be used, I've decided to use LEAN for its simplicity, low storage overhead, and featureset. You can find out more about it here: http://freedos-32.sourceforge.net/lean/

When all's said and done, the operating system should be portable to any processor system that meet or exceeds the hardware requirements.

Comments

Post a Comment

Popular posts from this blog

HP-125 Floppy Drive Emulation

A 'back burner' project I have in mind is to repair an old HP-125 computer I picked up at a thrift shop quite a while ago. This computer has no onboard storage drives, instead coming paired with an HP-82901M floppy drive unit , which communicates over HPIB/GPIB/IEEE-488 (whatever you want to call it). These drives are either pure unobtanium, or are downright bankrupting, so I need to find a way to emulate it. My requirements are as follows: Standalone operation, not requiring another computer to emulate Low cost parts, or using mostly parts I have on hand (Optional) Multiple uses, I don't want this to be a one-trick pony While I've learned how the GPIB protocol works, I have no idea what the command set is that either the HP-125 and/or HP-82901M speaks. I've found mention of the HP-82901M using the Amigo command set, as introduced with the HP-300 "Amigo", on this page about emulating an Amigo-compatible drive with a modern PC . That project requir...
1 comment
Read more

EEPROM Programmer

So, I'll be needing an EEPROM programmer in order to actually provide some startup software for my Z80 computer. I intend to make one using a set of shift registers, and a couple optoisolators, so that I can use any microcontroller with 8 I/O pins (7 output, 1 input), assigned as follows: Input: 1 = Data Read Output: 1 = Address/Data Write 2 = Shift 3 = ~WE 4 = ~CE 5 = ~OE 6 = ERASE/VPP (EEPROM/EPROM) 7 = Read Data The design will be as such that any microcontroller that uses either 3.3V, or 5V I/O can safely operate it. An interesting design requirement involves needing to have either 3.3/5V or 12V sent to the ~OE pin of an EEPROM, as the 5V signal is used to read from it, but the 12V is required in order to erase it. A possible solution will be to use a diode to prevent the 12V signal from feeding back to the microcontroller, and an optoisolator to gate the 12V to the same pin during an erase cycle. To obtain the 5V and 12V power rails, I will use a simple regulat...
Post a Comment
Read more

Introduction

This blog is intended to showcase my electronics and computer projects, as well as educating about related concepts. I currently have an ongoing project consisting of an 8-bit computer I call Zephyr (because I'm bad at coming up with names). Details as follow: CPU: Zilog Z80 rated to 10MHz (Currently running at 625KHz) Memory: 8KB of ROM, 32KB of RAM with room for expansion I/O: Serial Currently it doesn't do anything since I need to create an EEPROM programmer, which I plan to make using shift registers and a controller of some variety. I also have plans to create another 8-bit computer project called CosNaut (Again, bad at names) using an RCA 1802 'COSMAC' CPU, though anything else is not set in stone. Will post updates as necessary.
Post a Comment
Read more