Trying to receive a long STRING via ExtendedFDSerial.SPIN

DavidM

HI,

I am having trouble receiving a string back from the UMP3 Player.

I am sending the UMP3 a command "PC V" which asks for the units software version info.

This string I think is up to 24 characters long plus a delimiter character at the end">"

I am using the ExtendedFDSerial Object as follows

Serial.RxStrTime (20,000, rxData)

The reason I have 20000 for the timeout ( which I believe is 20 seconds) is that the SD Card of the UMP3 player needs time to LOAD before any commands are recognized. The manual says up to 20 seconds, but it usually is about 3-5 seconds. Anyhow, this isnt the problem,

Q1) the problem is I am trying to get the data ( the string from the rxdata) back to my main program.

here is my method for initilising the MP3 Player of which I want to get the PlayerVersion info string and display it on my LCD ( which I have just figurered out).
Just as a note I can send commands to the ump3 player such as play stop etc and this works fine, so everthing is connected and functioning.
I am using a pointer to the "PlayerVersion" variable which is defined in my main object by using @PlayerVersion which is defined as

MAIN OBJECT
 
VAR
  BYTE PlayerVersion[noparse][[/noparse]25]
PUB
 IF (uMP3.Init (rxpin,txpin,0,baudrate,@PlayerVersion)==TRUE)
  '' then show the player version variable on an LCD display   
  '' else show that there is no player found

My uMP3 Object

VAR

  BYTE RxData[noparse][[/noparse]25]

PUB Init ( vRxPin, vTxPin, 0, vBaudRate, PtrPlayerVersion) : Status

 Serial.Start ( vRxPin , vTxPin, 0, vBaudrate) : Status | rxData
 Serial.SetDelimiter (">")
 Serial.RxFlush
 Serial.Str(STRING("PC V"))
 Serial.Str(STRING(13)

 Serial.RxStrTime(20_000,RxData)
 IF (rxdata<>0)'' check if there is any data
  Status :=True
  '' do something here with the actual rx data to get it back as a string to the PlayerVersion variable"<---- THIS IS THE PART I NEED SOME HELP WITH [img]http://forums.parallax.com/images/smilies/smile.gif[/img]
 ELSE
 Status :=FALSE
RETURN Status

Any help would be great as I am totally confused with strings and SPIN!

regards

DaveM

StefanL38

Hello David,

in SPIN strings are seen as a "chain" of bytevalues inside the RAM. These bytevalues are the ASCII-codes of the characters of the string

In programming you can access such a "chain" with an array like you defined it

VAR
  BYTE PlayerVersion[noparse][[/noparse]25]

  Serial.Str(STRING(13)  '<--- here one closing-bracket is missing does this compile ?

RxStrTime can receive a string with maximum 15 bytes like the comment of the method says

for a string of 25 bytes you have to change some values inside the
file FullDuplexSerial.spin which is used by the Extended_FDSerial-object
AND the datain-array AND inside RxStrTime

This is not trivial but you can do it.

Then for receiving the string by RxStrTime the parameter of the methodcall has to be the POINTER to that string

   Serial.RxStrTime(20_000,PtrPlayerVersion)

another solution depending on your baudrate might be to use a loop that receives single bytes and transfers these bytes to your array PlayerVersion


accessing the bytes in the array looks like this

  PtrPlayerVersion := @PlayerVersion
  index := 0

  repeat until receivedByte == Delimiter
    receivedByte := Serial.Rx
    byte[noparse][[/noparse]PtrPlayerVersion][noparse][[/noparse]index] := receivedByte
    index++

  byte[noparse][[/noparse]PtrPlayerVersion][noparse][[/noparse]index - 1] := 0 ' finish with a zero instead of delimiter

byte[noparse][[/noparse]PtrPlayerVersion][noparse][[/noparse]index] is an absolute adressing

PtrPlayerVersion := @PlayerVersion means store RAM-ADRESS of bytearray PlayerVersion in variable PtrPlayerVersion

byte[noparse][[/noparse]PtrPlayerVersion][noparse][[/noparse]index] := receivedByte

means store value of variable receivedByte at RAM-Adress PtrPlayerVersion + index

example

bytearray PlayerVersion is located in the RAM at adress 20.480

index has value 5

variable receivedByte contains the value 65 (ASCI-code for "A")

then byte[noparse][[/noparse]PtrPlayerVersion][noparse][[/noparse]index] := receivedByte

stores the value 65 at RAM-adress 20.480 + 5 = 20.485

and if you want to show this "A" on the LCD you have to code

  index := 5
  LCDSerial.tx(byte[noparse][[/noparse]PtrPlayerVersion][noparse][[/noparse]index])

or if you want to show the whole string

LCDSerial.Str(PtrPlayerVersion)

in SPIN strings can only be represented by bytearrays
and you are accessing them via the POINTER to the RAM-Adress where the bytearray is stored

this explanation is semi-extended

if you have more questions about feel free to ask again

best regards

Stefan

Post Edited (StefanL38) : 4/9/2008 7:53:25 AM GMT

DavidM

Hi Stefan!


thanks for the extensive explanation! I really appreciate it.

A1) I left accidently left off the closing bracket , as I had to retype my code into the browser.

MODIFY the FD SERIAL OBJECT - OPTION

Maybe not for me just yet, Unless someone else has done this? Is there a reason that its only 15 bytes?

I like your second option where I just receive one byte at a time. I am running at 9600 baud so this should work.

Also.

There is another command for the MP3 player that gets a "list of songs" from the player, this can contain a lot of data so I will try out your "One byte at a time approach.

In regards to the LCD , I have my own code which works so I am not worried about that.

Again thanks for the great explanation!

Regards

Dave M

groggory

If you're using this semi-convoluted process on a regular basis to output to the LCD, you should probaly make a method that does it for you. Create some reusable code

DavidM

Hi groggory

I am not sure what you mean, I already have my own object that has all the commands for working with my LCD. Which is totally re-usable, I also said that the LCD was not the problem


Thanks

Dave M

DavidM

HI,

Ok I have it all working.

Lesson Learned

Always check that you are sending the right command to the serial device before calling for help!

I was using "PC V" when it should of been just been "V" , !!! Silly me.

I used the index increment method you suggested and received 1 byte at a time.

But I still was getting gibberish on my LCD as it did not like receiving a byte "String"

This was fixed by using the following code..

and for the LCD

LCD.DisplayString (@PlayerVersion, 1, 1) <-- I had to use a pointer here as well!!

and I received more data than I needed so I CUT-OFF the remaining data by setting the 6th byte to 0

byte[noparse][[/noparse]PtrPlayerVersion][noparse][[/noparse]6] := 0

I also managed to get the directory listing from the SD card using the same code!

Thanks for the help

Regards
Dave M