Embedded Strings in your Code Space

[mytekcontrols]

Thanks for the heads up on the PDS. I'll check go check it out. Although on the current project I extremely doubt I'll be jumping ship (... I can almost see the shore as we speak). However on another project, It might certainly be a consideration. How is the optimization of the code it produces?

Also as I said in my previous post, reliability plays a key role in my choice of programming tools. I tend to stick to what works, and usually find work arounds for minor ommisions. Case in point; the lack of string handling ability in PBP I quickly resolved by taking a different approach. At first I was stumped at not being able to set up a string variable that I could later pass to an I2C routine. Of course the solution came in the form of using lookup tables as shown below (printascii would go to a separate print routine for output, in my case a specialized I2C routine).

For y=0 To 255
Gosub mesghello
If ascii = Null Then exit
Gosub printascii
Next y

mesghello: Lookup y,["hello world",Null],ascii
Return

In my 6502 assembler days, I used a routine that would pop the return address off the stack, increment it by 1 to pick up the start of the ascii data to be sent, send the data, and then modify the RTS to return directly following the ascii data (next example).

jsr printascii
.byte "hello world",Null
-- rentry point upon return from printascii routine --

Much simpler, and some what more readable when looking at the source code (the messages appear where used, and not in a later table). However for messages that would be reused several times through out a program, the table approach is preferred in order to save code space. Unfortunately I haven't figured out a similar method that would work either within PBP or as an @asm script (can't pop the stack as far as I know).

I ran a suggestion by the makers of PBP about the possibility of including something like the LCDOUT command maybe in the form "BYTEOUT var{,item...} example:

ascii var byte[255]

BYTEOUT ascii,"hello world",Null
Gosub print ascii


printascii:
For y=0 To 255
If ascii[y] = Null Then Return
Gosub sendascii ' send character by whatever method desired
Next y
Return

This would yield something similar to the 6502 assembly example.

Anyway getting back to the original topic so to speak; picnaut thanks again for your sugestion about PDS.

[Darrel Taylor]

mytekcontrolsm,

Using a Lookup for strings can use up a huge amount of code. And I believe I may have the solution you're looking for.

How to store and retrieve strings in Code Space

Another person that I helped out a while back had his 877 completely maxed out with Lookups for strings to be displayed on an LCD. After converting them to the STRINGS in CODE format, it only took up 1.5K words. Leaving 6.5K for more program. We were both amazed.

And, I too will not be Jumping ship anytime soon. PBP is just to good.

Darrel

[Bruce]

Nice job Darrel, and thanks for the excellent resource. I've used several of
your routines on various projects.

Here's something similar for the 18F series.

DEFINE LOADER_USED 1
DEFINE OSC 4

ptr_pos	VAR BYTE
temp	VAR BYTE
x	VAR BYTE

Main:
   CALL USART_Init
   ptr_pos = 0
   CALL Start
   ptr_pos = 16
   CALL Start
   ptr_pos = 48
   CALL Start
   ptr_pos = 176
   CALL Start

Done:
   GOTO Done
    
ASM
_USART_Init
   movlw   B'00100100'   ;initialize USART
   movwf   TXSTA	 ;8-bit, Async, High Speed
   movlw   .25           ;value for 9600 bps @ 4MHz
   movwf   SPBRG	 ;set SPBRG for 9600 bps @ 4MHz
   movlw   B'10010000'   ;enable USART
   movwf   RCSTA
   return

;----Lookup & send text messages--------------------------
_Start
   movlw   UPPER msg_table
   movwf   TBLPTRU
   movlw   HIGH msg_table
   movwf   TBLPTRH
   movlw   LOW msg_table
   movwf   TBLPTRL
   movf    _ptr_pos,W	;prt_pos must hold message address
   addwf   TBLPTRL,F
   clrf    WREG
   addwfc  TBLPTRH,F
   addwfc  TBLPTRU,F

Next_Char
   tblrd   *+
   movff   TABLAT,_temp
   bra     Test_EOM      ;test for EOM character
	
Continue
   movf	  _temp,W	 ;move temp to w
   movwf  TXREG		 ;send it
   btfss  TXSTA,TRMT	 ;wait for data TX
   goto   $-2
   bra	  Next_Char      ;fetch next message character from table
	
Test_EOM
   movlw  "~"            ;check for EOM character
   cpfseq  _temp, 1	 ;compare temp with w, if temp = ~ then end			
   bra     Continue      ;no EOM, so continue
   movlw   "\r"		 ;move data into TXREG
   movwf   TXREG	 ;send carriage return
   btfss   TXSTA,TRMT	 ;wait for data TX
   goto    $-2	
   movlw   "\n"		 ;move data into TXREG
   movwf   TXREG	 ;send line feed
   btfss   TXSTA,TRMT	 ;wait for data TX
   goto    $-2
   return                ;finished with message, return to caller
ENDASM

ASM
msg_table	; Message strings
   data	" Message #1~    ";Message #1 starts at msg_table 0
   data	" Message #2~    ";Message #2 starts at msg_table 16, etc,
   data	" Message #3~    ";32
   data	" Message #5~    ";48
   data	" Message #6~    ";64
   data	" Message #7~    ";80
   data	" Message #8~    ";96
   data	" Message #9~    ";112
   data	" Message #10~   ";128
   data	" Message #11~   ";144
   data	" Message #12~   ";160
   data	" Message #13~   ";176
ENDASM

[Darrel Taylor]

Now there's an endorsement I can be proud of.

Thanks Bruce!

[mytekcontrols]

Thanks Darrel and Bruce for your great examples. I would have to say I like Darrel's approach the best, since it seems less cryptic as to what the messages are (i.e; you can give them meaningfull names). Also I like the idea that they can be located anywhere in the program (kinda like my 6502 example). However I am using an 18F252 for my project, and apparently this approach wont work with a 16 bit processor. Any ideas how this could be changed?

[Bruce]

' Text message addresses w/specific names
Intro CON 0
PumpOn CON 16
PumpOFF CON 32 ' etc,,

   ptr_pos = Intro     ' print intro message
   CALL Start
   ptr_pos = PumpON ' print pump on message, etc,,,
   CALL Start

You now have meaningful names for your strings. It's not that cryptic once
you've played with it a bit. The 18F series are easier to code in .asm than
16F parts.

Make your strings as long as you like. That was just a quick/simple example.

I don't have an example for placing strings all over code space since I would
never do that. PBP library functions & my app code get first pick. Huge
chunks of text messages get the left-overs at the bottom...;o]