Is there a better way...

I have a device that is completely controlled via RS-232. The commands to make the PIC do something, like read ADC, change levels of output pins, read SPI devices, etc. is all controlled by 3 letter commands from a PC. I use the HW uart on the PIC chip to load the data into a circular buffer and then look for a cr as a terminator. Then in my code I used multiple IF/THEN lines to match a valid command and then a subroutine to perform the action. The part that bothers me is the multiple IF/THEN about 20 of them that look like this:

IF chrbuf(0)="R" AND chrbuf(1)="T" AND chrbuf(2)="F" THEN GOSUB xxxxx
.
.
Is there a better or cleaner way to decode the three letter commands than using long multiple IF/THEN statements?

Terry

How about a checksum of the first 3 characters and a select case with the checksum?

Not sure about the checksum.
Wouldn't RTF and FRT end up the with the same number?

It depends on the letter combinations you need, but if there are common letters between the commands, maybe ...

Code:

IF chrbuf(0)="R" THEN IF chrbuf(1)="T" THEN IF chrbuf(2)="F" THEN GOSUB RTF IF chrbuf(2)="M" THEN GOSUB RTM IF chrbuf(2)="R" THEN GOSUB RTR ELSE IF chrbuf(1)="Q" THEN IF chrbuf(2)="P" THEN GOSUB RQP IF chrbuf(2)="C" THEN GOSUB RQC IF chrbuf(2)="A" THEN GOSUB RQA ENDIF ENDIF ELSE IF chrbuf(0)="T" THEN IF chrbuf(1)="T" THEN IF chrbuf(2)="F" THEN GOSUB TTF IF chrbuf(2)="M" THEN GOSUB TTM IF chrbuf(2)="R" THEN GOSUB TTR ENDIF ELSE IF chrbuf(1)="Q" THEN IF chrbuf(2)="Z" THEN GOSUB TQZ IF chrbuf(2)="S" THEN GOSUB TQS IF chrbuf(2)="1" THEN GOSUB TQ1 ENDIF ENDIF ENDIF

Thanks for the ideas, it seems like PBP really needs some string capability where then the "case" statement could be used which I think would then be a natural for this type of application.
Terry

There are lots of different ways... not nescessarilly better, just different...

Take a look at this example posted OMG!!! Three years ago!!!

http://www.picbasic.co.uk/forum/showthread.php?t=573

It does pretty much what you're doing, receiving a command string terminated by a CR, then parsing that string for embedded commands to act upon... just another angle on the same theme...

So, as another example, if all your commands are say 3 characters long each, then stick them all together into your program as a long string (who says you can't build strings with PICBasic!!!) with a separator character between them (you can have that "string" in EEPROM, or within your program code)... eg...

Code:

iRobotActions: ASM db 0x00,"HUG" ; Greeting db 0x00,"EAT" ; Recharge Batteries db 0x00,"FLY" ; Go Somewhere db 0x00,"KIL" ; Prime Directive db 0x00,"RTM" ; Learn db 0x00,"SEX" ; Have Fun db 0x00,"DIE" ; Wait for armageddon ENDASM

...then simply scan that "string" to find the position of the command you seek (which in turn will give you a number based on the position of that command within the string). Then armed with that number you can then simply use your case statement (or even a bunch of simple IF's). This basically gives you unlimited scope for your embedded commands.

nb. You need a separator between the commands, otherwise a random jumble like 'EXD' as the last two characters of 'SEX' and the first of 'DIE' would return a result.

Quote:

Originally Posted by Melanie

There are lots of different ways... not nescessarilly better, just different...

Take a look at this example posted OMG!!! Three years ago!!!

http://www.picbasic.co.uk/forum/showthread.php?t=573

It does pretty much what you're doing, receiving a command string terminated by a CR, then parsing that string for embedded commands to act upon... just another angle on the same theme...

So, as another example, if all your commands are say 3 characters long each, then stick them all together into your program as a long string (who says you can't build strings with PICBasic!!!) with a separator character between them (you can have that "string" in EEPROM, or within your program code)... eg...

Code:

iRobotActions: ASM db 0x00,"HUG" ; Greeting db 0x00,"EAT" ; Recharge Batteries db 0x00,"FLY" ; Go Somewhere db 0x00,"KIL" ; Prime Directive db 0x00,"RTM" ; Learn db 0x00,"SEX" ; Have Fun db 0x00,"DIE" ; Wait for armageddon ENDASM

...then simply scan that "string" to find the position of the command you seek (which in turn will give you a number based on the position of that command within the string). Then armed with that number you can then simply use your case statement (or even a bunch of simple IF's). This basically gives you unlimited scope for your embedded commands.

nb. You need a separator between the commands, otherwise a random jumble like 'EXD' as the last two characters of 'SEX' and the first of 'DIE' would return a result.

Could you please help with how to search this string to get the location number?
Many Thanks
Steve

db?? nah... grandma tricks, there's a better way, use the following...

http://www.pbpgroup.com/modules/wfse...p?articleid=10

Quote:

Originally Posted by mister_e

db?? nah... grandma tricks...

Hmm, from the avatar I don't think Melanie is so much old grandma...!

Ioannis

;) yeah i know... just kidding a little bit ;)

I figure the 'Embedded Strings in code space' stuff will be somehow easy to implement, and will eat less code space.