Re: IKBOCS - Object Oriented Operating System

From: Ben Yates (anoneds_at_netscape.net)
Date: 05/25/04 

Date: 25 May 2004 10:33:02 -0700

stephen.webb@bregmasoft.com (Stephen M. Webb) wrote in message news:<34e1ce0c.0404270850.2528a997@posting.google.com>...
<snip>
> but things are getting a little foggy now.

Yes, a little bit.

In reality, the TI contained TI BASIC written in a mix of GPL
(Graphics Programming Language) and assembly. Most of it was GPL.

There was a GPL interpreter coded in 9900 assembly in the ROM. GPL was
one level above assembly. It provided a level between the actual
hardware and the software that allowed you to treat the various
memories (CPU, Video RAM, GROM/GRAM) in the same way. In assembly, the
latter two would be written and read across ports. GPL was stored in
GROM ("Graphics" ROM). So, Basic is written in another low-level
interpreted language (GPL) with assembly subroutines. So, a Basic
program is interpreted by a Basic interpreter being interpreted by a
GPL interpreter - double interpretation.

The "Monitor" is the portion of the OS in GROM 0 that contains the
powerup code, initializing devices and building the Title Screen. TI
Basic is in Groms 1&2.

There is 256 bytes of CPU RAM for the tms9900. The 16k useable by TI
Basic is shared with the Video chip, the tms9918a. Programs and Data
for TI Basic programs are stored in the Video RAM, which is accessible
a byte at a time over the ports.

You had to buy Extended Basic and a 32k card to have a Basic that
could access CPU RAM. The 32k card was divided into an upper 24k
portion (this is where your program and numeric variables were
stored), a lower 8k (for assembly routines), and string space was
still in Video RAM.

Ben

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