c-pod Specifications

USB Part 1: Hardware Latencies

The latency for sending an event code depends on the baud rate selected through the driver. At the recommended 115,000 baud rate, the three byte command needed for sending an event marker takes 0.36 milliseconds to transfer.

Once received, c-pod processes the command and produces the output in less than 0.1 milliseconds.

USB Part 2: Software Drivers

For sending event markers via USB, software where the real bottleneck is.

The delay is 2ms, jitter-free when using:

• Cedrus-provided C++ and Python pyxid2 libraries.
• Off-the-shelf software that uses one of these two libraries, e.g. SuperLab or PsychoPy.

The delay is ±5 to 6 ms when using other software such as E-Prime.

WHY: c-pod is compatible with two different USB drivers. The Cedrus-provided libraries use a high precision driver provided by the manufacturer of the USB interface chip used inside c-pod. The other driver is less precise but can emulate a serial port; this makes it compatible with a wide range of software such as E-Prime.

TTL Output

Maximum current draw is 50mA maximum for c-pod, and 5mA maximum per pin.

Firmware Capabilities

c-pod offer these advanced built-in features:

• Asynchronous Output
  With this capability, your software does not need to wait for the duration of the pulse before doing other things – it simply sends a command to c-pod and moves on.
• Pattern Generator
  You can ask c-pod to generate periodic pulses on specific output lines. While it’s doing so, c-pod can continue to respond to commands that it receives from you via USB.
• Scheduler
  A truly unique feature that’s best described by an example: you want to present a movie (or audio) and need to send event markers at specific points during the movie. With c-pod, you can build an event schedule, e.g. send a 10ms pulse at T+200ms and a 15ms pulse at T+354. When the movie starts, you send a command via USB to run the schedule. c-pod will then produce a 10ms event marker 200ms later, and another 15ms marker 354ms after receiving your command.

Software Support

All the firmware features described above are supported by our C++ library. Some are supported by our Python and Matlab libraries as well, and we can add support for other features upon request. All libraries are open source and on GitHub.

The raw commands that c-pod accepts are fully documented.