This is a first step toward separating the CPU core and UI. The UI program
starts the CPU core as a subprocess and communicates through its standard input
and output. The protocol is deliberately simple at this point. Each bus request
from the core is exactly eight bytes:
+-------------------------+
| cpu cycle counter high |
+-------------------------+
| cpu cycle counter |
+-------------------------+
| cpu cycle counter |
+-------------------------+
| cpu cycle counter low |
+-------------------------+
| 0x00=read / 0x01=write |
+-------------------------+
| address high |
+-------------------------+
| address low |
+-------------------------+
| value (unused for read) |
+-------------------------+
A single-byte response from the UI is required for a read request, and a
response must not be sent for a write request.
The above protocol is expected to change. For example:
- the UI should tell the CPU core which address ranges are of interest
- needs ability to send memory images to the core (both ROM and RAM)
The stream communications is currently buggy because it expects that all eight
bytes will be read when requested (that is, partial reads are not handled). In
practice, this seems to work okay for the moment.
To improve portability, it may be better to communicate over TCP sockets
instead of stdin/stdout.
