New OS for the C64U

Hallo allemaal,

This is another episode of writing my own OS for the C64U. As said 
before,I wanted to use a minimal Kernal and no BASIC. I mentioned my 
first susscess but then I found out Ineeded something to accept 
commands. I realised that the BASIC interpreter could serve this purpose 
so I added the BASIC ROM and started to throw out everything not needed. 
I changed some small things:
- If the C64 recognises a keyword, it acts on it. So LISTZZZ will 
trigger LIST. I added a routine that expects a space, zero or '=' at the 
end of the keyword.
- Originally a keyword is converted in a code and later everything is 
decoded. My idea is that the first word is the command and no further 
crunching is needed. So when a keyword is found, it is executed at once.

What are the supported keywords the? First you have to know that the 
total of ROM is now roughly 6140 bytes so I have 2000 bytes left to 
spend on internal commands. Writing my OS for fy PC 10/20-III machines I 
had a very small 'COMMAND.COM', called CONTROL in my case, so every 
command had to be loaded. But then I ran into a problem: after changing 
a directory, I lost my access to my commands! So I'm busy to include 
PATH.

So I will include PATH here from the beginning. I'm sure 2000 bytes is 
enough to include it in ROM and maybe more commands are possible. The 
next one I can think of is CD/CHDIR. Another possibility: the C64U 
supports the REU. Supporting the needed commands to handle it in ROM 
will speed up things.

To be continued....


-- 

Kind regards / Met vriendelijke groet, Ruud Baltissen

www.Baltissen.org