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Updated Troubleshooting (markdown)

mike w 2016-09-11 16:48:19 -04:00
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Troubleshooting.md

@ -16,4 +16,17 @@ You don't; see previous question. `/dev/tty*` is the Linux kernel's driver inte
## I am using an Arduino Uno, Sparkfun Pro Micro, or other Arduino and "if (Serial)" doesn't work. ## I am using an Arduino Uno, Sparkfun Pro Micro, or other Arduino and "if (Serial)" doesn't work.
Some Arduinos use the DTR line to determine serial channel readiness. In your Android code, call `setDTR(true);` Some Arduinos use the DTR line to determine serial channel readiness. In your Android code, call `setDTR(true);`
## When reading a message, why don't all bytes arrive at the same time?
The protocol layer does not guarantee all bytes will arrive in a single message. In fact the protocol layer doesn't have any knowledge of what your "message" is — it is just an interface for sending a serial stream of bytes.
For example, to receive a 100 byte string, you might read 64 bytes, then 36 bytes, instead of a single message of 100 bytes.
You need to account for this problem when designing your protocol. Some common techniques:
* Fixed length messages: If you a message is always going to be 100 bytes, just keep reading until you have all 100.
* Length-prefixed messages: Prefix every message with a fixed-length `size` value; your message is complete after you've read `size` more bytes.
* Newline-terminated messages: Read until you see a `\n` (or any other "terminal" character).