Teensy 3.1 UART

[bigpilot]

Looking at the specs it seems the Teensy 3.1 and 3.0 both have 3 UARTS but the Teensy 3.1 has 2 UARTS with FIFO's whereas the Teensy 3.0 only has 1.

What would be the advantage of having a FIFO? Less dropouts during interrupts? I'm planning to use the Teensy for a model rocket which needs two serial connections for the GPS and telemetry. Would it make any difference to have a FIFO in this application?

 

[stevech]

main benefit of UART FIFO: Reduced interrupts per second from the UART. Important at rates like 57600 and up. In one interrupt, a properly written UART handler can accept many bytes from the FIFO (UART RX) or load many into the FIFO (UART TX). Example: 16 byte FIFO hardware. Interrupt when filled to 10 on RX. Interrupt rate on RX is now 1/10th what in would be without FIFO.

GPS is often at 4800 baud so that's not a high rate. Telemetry, assuming it's wireless, is probably not high rate either.
Teensy 3.1 UART handlers support FIFO as I recall. The use of FIFOs is "transparent" to your software, other than the affect on interrupt rates.

 

[PaulStoffregen]

Steve is absolutely correct. The FIFO make Serial1 and Serial2 more efficient, requiring about 1/4 as many interrupts.

Teensy 3.1 is already very fast, so at lower baud rates it makes very little difference.

 

[stevech]

But look into the details... some UARTs on Teensy 3.1 lack a FIFO.

 

[bigpilot]

Ok thx, it probably doesn't make that much difference for my application, I gather.

 

[bsculley]

Hi, hope this is a good place to post... I'm trying to get ROSSerial running between Teensy 3.1 and Beaglebone Black.

I installed ros_lib and downloaded the "Hello World" example to Teensy. It runs, but there doesn't seem to be any choice as to which UART to use.

Does anybody know which pins the output should appear on? If anyone has actually done what I am attempting, I'd love to hear about it!