FAST Forth Native-Language Embedded Computers

Listing Six. Even add timing diagrams with a text editor.
U I L
(
)
( NORMAL )
( A B C F G A . . . 1
( 1
( 1
( IF JUMPED GUN 1
( A B CD E G A . . . 1
Listing Seven. Use of binary when individual bits are of interest.
: SYNCSERSETUP ( -- )
[BI
VIADDRB C@ 1 OR VIADDRB C! ( SET PBO AS OUTPUT FOR STROBE LINE. )
VIAACR C@ OOOlOlOO OR ( ENABL SR TO SHIFT OUT UNDR T2 CTRL. )
1101O111 AND VIAACR C! ( DECR AT @2 RATE. )
00100100 VIAIER C! ( DISABL SR-EMPTY & T2 IRQs. )
( SET T2 FOR ABT lookHz SHFT RATE, LO )
[HI 8 VIAT2CL C! ( BYT 1ST. T2 GETS RST AUTOMATICALLY )
0 VIAT2CH C! ; ( SO ITS NOT REALLY 1-SHOT IN SR MODE )
with the number of bytes already backed over. If there is
disagreement, it has not arrived yet at the NFA, and it
needs to keep looking. You might see right away that a few
combinations could still fool it. Those are easy enough to
determine and avoid.
A text editor will allow you to use the graphics
characters for diagrams in your comments. The diagrams
in Listing Five are out of an application I did a couple of
years ago. They preceded my keyboard-scan code in
Listing Four-a.
Where an explanation of timing is appropriate to
understanding code, you can even include a timing
diagram. For example, following a timing descriptior! in
the comments on a recent project, I put in the diagrams in
Listing Six to graphically summarize.
The source code should be more than just compiler-
needed input-it should be the major software document.
The diagrams are worthless to a compiler, but are priceless
to someone who has to come along later and figure out
how to update the code.
A text editor like the Norton Editor can also allow you
to look at two files at once with a split screen, and to copy
portions from one to the other, test portions for differ-
ences, etc. The transfer between files is transparent as you
move the cursor with the mouse.
You can scroll. You can use block markers as book
marks which the editor can find instantly after you have
been looking at something elsewhere in the file. You can
use different modes of search, or search-and-replace,
including reverse and case-insensitive. The searches will
be extremely fast, since usually the whole file is in RAM
and disc access is unnecessary. You can flip the case from
the cursor to the beginning or end of the line to transfer
from upper- to lower-case (or vice versa) without retyp-
ing. You can reformat a paragraph, which is useful for
comment paragraphs when you need to insert or delete
something in the middle without messing up all the line
lengths.
If you can forego the few advantages of screen files, a
text editor can give you far more flexibility than the screen
editors I've seen.
More Vertical Alignment
Listing Seven shows a colon definition I used to set up
a synchronous serial port on a 65C22 VIA (versatile
interface adapter) IC. The register names came right out of
the data book, which has register diagrams showing the
bit-by-bit functions. We want to pay attention to individual
bits (not the overall number they make up), and we want
to mask and set or clear individual bits; so it makes sense
to use binary and line them up vertically, just as our
second-grade teachers taught us to do for addition.
Sometimes, immediate do-nothing words are very
helpful for clarifying code. You could have words like
: SAMPLES ; IMMEDIATE
: k ~ z ; IMMEDIATE
to use in a sequence that plays back a specified set of
samples at a specified rate, like
TBLl 2000 SAMPLES 8 kHz PLAYBACK
Alternatively, SAMPLES could, for example, store the
number on the top of the stack for PLAYBACK to use, so
the net stack effect of 20 0 0 SAMPLES would be ( -- ).
Now and then, we hear talk of programming languages
or command structures that are very "English-like," as if it
were a plus. Frankly, English is a lousy pattern for a
programming language to follow. For technical communi-
cation, it's far better than some other languages, yet
confusion still abounds.
March 1994 April 24 Forth Dimensions