It will consist of the following parts:
- processor in the spirit of the #1 Square Inch TTL CPU
- a simple ALU
- some address registers
- at least 256 KByte RAM
- flash-ROM for booting
- VGA text output 80 * 25 chars
- VGA color output (resolution TBD)
- PS/2 keyboard input
- user-accessible I/O pins (footprint of Arduino shield)
- a sound system
- serial flash (16 or 32 MByte) for storing all your programs.
The text mode will have several (probably 4) colors, and the goal for video is freely mixing of text and full color mode.
At this moment, the idea is that the CPU and the video part will operate quite independent. The CPU might even be a separate pcb that is placed on top of a "motherboard", that has the memory, video and other I/O.
The CPU will probably be around 32 TTL parts and a microprogram Flash.
The instructions will be implemented in microcode. There will be two main instruction sets:
- The native KOBOLD instruction set has highest execution speed and very good code density. The instructions are similar to PDP11 instructions. The instructions can access 1MByte of memory.
- The K11 instruction set is binary compatible with the PDP-11 instructions. It is kept in mind, but will only be given full attention after most other goals are reached. It might become a separate project.
The microcode can be easily reprogrammed with a Raspberry Pi as programmer (just as with the 1 Square Inch TTL CPU ). The microcode Flash is large enough to accomodate a lot of microcode.
A Raspberry Pi can be connected, that can read or write files from or to the serial flash of the Kobold.
When enough supporting software is in place, the programs for Kobold can be developed on the device itself, perhaps first in BASIC and later in C.
- design the CPU
- pcb design of CPU with thru-hole components
- design the motherboard
- pcb design of motherboard
- some simulations
- order boards, and assembly
- hw fault finding
- pcb design of a small Kobold CPU in SMD version
- build or adapt a C compiler
- make system software. Might adapt an OS.
This is a work in progress, the logs will show the design steps....