Section 2 - Commodore Computers

May, May. 1982. Issue 24 2A
COMPUTE!
COMPUTEI 163
The reason that only the values from 0 to 127
are acceptable is that a byte with its most significant
bit (MSB, (MSB: $80$ 0 or 128) turned on is our signal that
this byte is IS to be the last character in the soft key
string. Obviously, ObvIOusly, you can rewrite this part, if you
desire, so that some other means is used to designate
the end of string stnng (a preceding length byte or trailing
zero byte are obvious alternatives). However, the
method chosen is simple and seems adequate for
most purposes. pu For the BASIC user, the soft
keys can be made truly 'soft'...
For the BASIC user, the soft
keys can be made truly 'soft'...
One more note before we get into implementation
details: since there are times when you u might
really
y want the graphics character "hidden" by a
soft key, I have designed an "escape" sequence.
Pressi ng "control-comma" (normally the graphics
Pressing "control-comma" (normally the graphics
heart character) signals to the soft key routine that
the next character is not /101 to be translated. Thus,
even the heart may be generated by pressing
even the heart may be generated by pressing
control-comma twice.
The NIHy·GrIHy
Nitty-Gritty
Program I shows the complete source of Easykey,
Program 1 shows the complete source of Easykey,
the program which implements all the features
mentioned above. The program is composed of
five primary parts.
mentioned above. The program is composed of
five primary parts.
The first part, with line numbers in the 2000-
2999 range, is used to hook the routine into Atari's
OS. First, rirst, we search the Handler Table looking for
the E: device. When we find it, we hold onto its
address and put the address of our replacement
driver in the table instead. Recall that the address
in HATABS H must be the address of the Handler
Routine Table. We copy the current table (presum
Routine Table. We copy the current table (presumably
the Atari default table, from ROM) to our
ably the Atari default table, from ROM) to our
NEWETBL (new E. table) and replace the entry
point for the get-a-single-character routine with
poi nt for the get-a-single-character routine with
the address of our new routine (NEWEGETCH)
less one (always required, see commentary on the
M: driver in my January column). We then change
LOM EM so BASIC won 't wipe us out and exit.
LOMEM so BASIC wont wipe us out and exit.
The second part of this process is the new geta-single-character
routine for the screen editor (E:)
device. Most of this code is copied directly from the
OS ROMs, the only exceptions being the branches
to locations in RON! and the call to the
get-
keyboard
to locations in ROM and the call to the keyboard
get-a-character routine (KGETCH).
The third part, NEWKGETCH (NEW Keyboard
GET single CHaracter routine), is the heart
of this whole process. Here is where individual
keystrokes are actually interpreted from their
hardware codes and characteristics charaCleristics to a more palatable
ATASCIIA TASCll code. But here, also, is where the
system is vulnerable to our machinations. Since
nothing "downstream" of the keyboard handler
(e.g., the rest of the E: driver, CIO, BASIC, etc.)
knows what happened at the physical keyboard
level, the calling routines will believe the keyboard
handler no matter what it tells them. thcm.
Actually, NEWKGETCH t is fairly simple. First
it checks to see if it is already processing a soft key.
If I f so, it simply hands the caller the next key of the
soft key's string. IfI f not, it goes and gets a real key
from the keyboard. If that key is a heart, it simply
gets the next real keyboard key and passes that
back to the caller (our "escape" clause). Otherwise,
if the keyboard key was not control-A through
Control-Z, then the key is returned to the caller
unchanged.
If the keyboard key was one of the definable
soft keys, its value is used to index into a table of
soft key string pointers. Here one last validity
check is made: if the string pointer is zero, the
keyboard key is returned to the thc caller and no soft
key string handling occurs. IfI I' a string pointer is
encountered, its address is placed in KPTR and
used to access all the characters in the string.
Note that zero bytes are translated to $9B (CR)
characters and that any character with its most
significant bit on terminates the string (by zeroing
the high order byte of KPTR).
The fourth part of this routine is simply the
above-mentioned table of soft key string pointers.
Note that we take advantage of the fact that the
assembler places zeroes into .WORDs (or .BYTEs)
which are undefined.
The last part, of course, consists of the actual
strings. Note the flexibility here. Control-D (label
SO), SD), for example, includes the modified CR character
($00) as also its last character by simply turning
onn the MSBit, producing a code of $80.
Soft Keys: Using Them From BASIC
Soft Keys: Using Them From BASIC
To conserve space and to show the flexibility of the
soft key system, I included strings for onlyy three
keys: control-D, which causes a disk directory
listing, control-S for "SETCOLOR," and control-P
for "PRI NT#." The simplest way to add more soft
for "PRI NT#." The simplest way to add more soft
key strings is to plllthem put into the source givenn
(with labels "SA" through "SZ," as appropriate)
and assemble the whole thing at an address
appropriate for your system.
But youu can add or change soft key strings