CODEWITHSUNDEEP
arduinoraspberry-piuart
NMilev
NMilev

Reputation: 77

Raspberry Pi and Arduino Mega 2560 UART behaviour difference

I've been trying to establish serial (UART) communication between a Raspberry Pi Model B Revision 2.0 (checked the model like described on this page) and Arduino Mega 2560. I made a service on the Pi that writes to UART and then expects a message and a coworker programmed the Arduino with an echo program. While they were communicating, I had trouble receiving data, meaning that it was clustered in 8 byte pieces and I had to introduce a timeout for waiting between them (I was actually as much as available and calling select()for the next cluster but it turned to be 8bytes a cluster, except for maybe the last one. As explained in a question I found on this site, the programmer is the one to take care of the protocol and can not rely that the whole message will be ready to read at once (that is logical). However, when I just connected Pi's TXD and RXD pins, no matter how much bytes I tried sending, it sends them in one go (I've gone up to a bit more than 256, that's more than enough for my purposes). I also have around 50 milliseconds of duration difference, measured directly from within the program, using gettimeofday() function.

So, could anybody clear things for me:

  1. Why is this happening?
  2. Is this difference in behaviour expected?
  3. Is there a potential problem in either of the devices (if that can even be concluded from the given information).

Of course, any additional information is welcome, in case I forgot asking something that is deemed important.

Upvotes: 0

Views: 282

Answers (1)

stuartnox
stuartnox

Reputation: 659

Why is this happening?

I tried some time back communicating Arduino-Arduino and Arduino-Pi. I faced some problems with UART communication. However, you might want to keep same Baud rate on both the devices. With Pi, you might need to trigger an event if you receive data from Arduino. On the other side, if you code runs longer, then you might lose some data i.e. your Arduino code is running something else while Pi sends data over UART.

Is this difference in behaviour expected?

Yes. Arduino is a microcontroller based device while Pi is microprocessor based (runs on OS)

Is there a potential problem in either of the devices (if that can even be concluded from the given information).

I don't think there could be any hardware problem unless it is not functioning at all.

Also, because of this issues, I switched from UART communication to SPI communication. This solved my problem completely.

Upvotes: 0

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