High Speed UART?

Technical discussions around xCORE processors (e.g. General Purpose (L/G), xCORE-USB, xCORE-Analog, xCORE-XA).
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mikef
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High Speed UART?

Postby mikef » Sun Dec 13, 2009 5:08 am

I've used the XMOS software UART on my XC-2, but only at 115200bps. Over winter break, I'm hoping to interface with my Bioloid Servos, the Bioloid bus typically runs off a 1Mbps serial connection.

All the documentation seems to state that 921000bps is the max speed of the example software UART, but I can't find anything that says why a 1Mbps UART couldn't be done.

Before possibly wasting time on this, anything I should be aware of? Is there some limit on pin switching that I'm not aware of? If necessary, I can drop the speed of the bus, but I'd rather run it at full speed if at all possible.

-Fergs
Heater
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Postby Heater » Sun Dec 13, 2009 8:34 am

I'm not familiar with limitations on the software UART perhaps there are some due to the way it is written.

If toggling/sampling the pins in software using timers or port counters is actually too slow then don't forget the ports can also serialise/de-serialise in hardware at far greater speed. Up to 32 bits of serial data can be clocked in or captured by the port hardware between reads/writes of the port by software. This is how it is possible to get up to USB and Ethernet speeds.

Take a look at the document "XS1 Ports: Use and Specification". Section 2.3 shows a 25MHz serial to parallel conversion.
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Bianco
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Postby Bianco » Sun Dec 13, 2009 2:31 pm

1Mbit/second should be no problem at all!
Maybe the way the baudrate divisor is stored in that software UART limits the baudrate.
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mikef
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Postby mikef » Sun Dec 13, 2009 5:56 pm

Thanks, that all sounds great. I'll be trying this out later this week (last exam of the semester is on Tuesday).

-Fergs

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