It will consist of the following parts:
- processor similar to 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 27 TTL parts and a microprogram Flash. (But now I am aiming for a full PDP11 instruction set, this will be more than 27.)
The instructions will be implemented in microcode. The first instruction set that I have in mind is similar to the PDP-11. Binary compatibility with the PDP11 is under investigation.
But the microcode can be easily reprogrammed with a Raspberry Pi as programmer (just as with the 1 Square Inch TTL CPU ), so it could also behave as another processor like the 6502 or Z80. 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....