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timing notes

Overview

This document is intended to give a general overview of the 37e12's speed capabilities. The 37e12 is not currently set up to be a high speed device, it doesn't do timestamping other than counter notification, It cannot set up an AtoD burst, and it runs all hardware request through the standard Linux kernel. In general this means that although process's on the 37e12's processor run fairly quickly,you will experience approximately a 10ms delay(the Linux scheduler freq) on any given blocking read, which will put the 37e12 task to sleep until data arrives. This delay is caused by the drivers kernel mechanism, in the future it may be bypassed by an RTAI driver, which would allow lxrt functions to wake much more quickly. The sections below provide more specifics.

AtoD

Firmware Rev1.3 does not provide for high speed AtoD samplings. It is intended for the reading low speed devices such as thermocouples, potentiatomers, etc. The firmware works by constantly sampling the AtoD and returning the most recent sample whenever it is requested. This version does no timestamping. That being said, the 37e12 hardware is capable of providing much higher sampling rates, the bottleneck is within the high level request/grant protocol communications, and the fact that the AtoD doesn't currently undergo any type of timestamping so it can't really be used for audio samples. If this speed is important to your application, please let us know as many of this boards software applications are based upon demand. Currently the targeted sector does not seem to warrant the engineering time, but let us know if this is not the case!

PWMs

Hardware PWM's (Port1) can support duty cycles from 0 to 100 at 367 - 65535 Hz.

Software PWM's (Port0) can support frequencies of 187 - 8334 Hz at 50% duty cycle reliably. reliable operations occur within: ((.0027>duty/freq) >.00006)&&(.0027>((100-duty)/freq)>.00006) Which basically says that no pulse(high or low) may be larger than 2700us or smaller than 60 us.

Currently there is no software control preventing this from happening.

See also:

E12_PWMControl

Counters

The 37e12 counters have been tested to be stable at up to 10KHz frequencies with all the counters running simultaneously. This limit is set by the 37e12 firmware.

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