On 5/29/18 5:13 AM, Jeffrey Birt wrote:
>>> Anytime a new scalar (i.e. non-array) variable is created, the
addresses of the array variables must all change to make room for the
new scalar variable.
So BASIC copies all the arrays to a new memory address? That does not
seem very efficient.
Hey Jeff,
Yeah, the M100 does a lot of stuff that is inefficient like this to
maintain it's RAM filesystem. Adding / removing any bytes from a BASIC
program will cause the ROM to copy all TEXT and .CO files to a new
memory address, plus any BASIC programs that exist past the edit.
Likewise, editing any TEXT document will cause the ROM to copy all .CO
files to a new memory address, plus any TEXT files past the edit point.
Actually when you enter TEXT, the ROM expands the .DO file being edited
such that it occupies the remaining free RAM. It does this by copying
all files past the edit point to the highest RAM location possible.
That way individual keystroke edits don't have to perform copy, copy,
copy operations. Then when you exit, it shrinks the file back to the
minimum size and copies .CO and higher RAM TEXT files back down to their
new location in RAM.
In general, files / Data in RAM are ALWAYS stored in the order and RAM
is copied as needed to ensure this order is maintained:
.BA
Unsaved BASIC program
.DO
.CO
BASIC scalar variables
BASIC string variables
BASIC array variables
The ROM maintains a RAM pointer containing the start address of each of
these location, and it has a routine to recalculate each of those
pointers that it can call as needed (i.e. when you want to edit a
specific TEXT file, etc.).
Ken
