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Topic: Serial transfers corrupted... (Read 2 times) previous topic - next topic

Anders 2009

Hi,
this is probably a newbie question, but I would really appreciate any pointers to help me take the next step in solving a "mysterious" problem I have with serial transfer of a binary data file (190 bytes) from Mac -> Arduino.

I have tried to search this forum and the net, but I haven't found anything similar. That's why I think it's me and not the platform...

In short, I am trying to transfer a binary file, using 9600bps, from a Procesing Sketch to my Arduino. Once it didn't work immediately I started debugging and I have now discovered that even if I just echo what I receive in the Arduino back, the data gets "corrupted" all the time. Please see the log sample and code below.

To make it dead simple I just send one byte at a time to the Arduino and then echo them back as soon as I read them. Should be fine, right?

Serial transfers of sketches etc. work perfectly, so I am a bit at a loss. Any ideas, anyone?

Thanks/Anders

[font=Courier New][size=11]
____ DEBUG OUTPUT (from Processing sketch)

Wrote byte:      -1      hex: FF
Wrote byte:      -1      hex: FF
Wrote byte:      1      hex: 01
Wrote byte:      2      hex: 02
Wrote byte:      54      hex: 36
Wrote byte:      -1      hex: FF
Wrote byte:      -1      hex: FF
Wrote byte:      1      hex: 01
[glow]Wrote byte:      66      hex: 42
Wrote byte:      117      hex: 75
Wrote byte:      115      hex: 73
Wrote byte:      115      hex: 73[/glow]
...

Read byte val: -1      hex: FF
Read byte, val: -1      hex: FF
Read byte, val: 1      hex: 01
Read byte, val: 2      hex: 02
Read byte, val: 54      hex: 36
Read byte, val: -1      hex: FF
Read byte, val: -1      hex: FF
Read byte, val: 1      hex: 01
[glow]Read byte, val: 65      hex: 41 <<<<< WHAT? Should be value 66 (see above)
Read byte, val: 115      hex: 73 <<<<< CORRUPT FROM HERE ON
Read byte, val: 3      hex: 03
Read byte, val: 23      hex: 17[/glow]
...


____ CODE THAT SENDS (Processing)

 byte b[] = loadBytes("binary.file");
 for(int i = 0; i < b.length; i++) {
   myPort.write(b);
   println("Wrote byte:\t"+b+"\thex: "+hex(b));
 }



____ CODE THAT RECEIVES AND ECHOS BACK (Arduino)

// Read one byte and acknowledge by sending it back
//
byte ACKRead() {
 while(Serial.available() < 1) {
   // wait for data
 }
 byte b = Serial.read();
 Serial.write(b);
 return b;
}[/size][/font]



PaulS

Just out of curiosity, what happens if you add a delay(5); statement between the Serial.read() and the Serial.write()?

Mitch_CA

It's possible that you're dumping too much data onto the Arduino serial port before it has a chance to read it.
Try some handshaking; don't push all the data unless Arduino is ready to receive it.
That's where I would suspect.

Anders 2009

Wow!, thanks for the quick replies!

@Mitch_CA:
I have been suspecting some kind of buffer overrun as well. The Arduino ref. says 128bytes serial buffer and I know I am sending more. Unfortunately it does not say what happens when the buffer is full on the Arduino side. Will it block the sender from sending more until buffer is depleted?, or will it start corrupt/overwrite? I was guessing/hoping that it would block the sender from sending more data. Maybe it doesn't.

I will try to add some primitive handshaking/ACK to see if things get better.

@PaulS
I will add the delay just to see what happens.

Thanks guys!/Anders

Anders 2009

Ok,
I tried adding the delay(5)-statement without any effect. Saw exactly the same error.

Will try to whip up some primitive handshaking now to prevent buffer overflow.

Surely, this must be something that has been solved before. Anyone knows a good library to use (like "safe serial transfer")?

/Anders

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