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Frequently Asked Questions on the PiXi


Q) Where can I buy one?

A) Please watch this space... We'll be making an announcement later this year (2013) on how you can get your hands on a PiXi (2.0)


Q) How much will it cost?

A) We're working to keep the cost as low as possible. RRP prices aren't yet available but our aim is to provide a reduced specification model "PiXi (2.0) Lite" that's available for under £40. The "PiXi (2.0) Std" version will support the full specification and will cost a little more. We’re also considering a super-lite version which would be priced under £30.


Q) Does it come with a power supply?

A) No, but like the Raspberry Pi, it’s designed to run off a USP phone charger, just power the Raspberry Pi with the PiXi connected to the Raspberry Pi’s 26-pin connector and the PiXi can take its power from the 5V power supply pin on the Pi’s 26-way connector. Alternatively, the recommended technique which allows you to do much more with the PiXi, is to use any 6.5V to 15V power supply capable of providing 12W or more, to power the PiXi (and the Pi) from the 2.1mm DC ‘Jack’ socket on the PiXi. It’s protected against reverse-polarity on the DC Jack socket too, just in case anyone accidentally gets the connections wrong when wiring up the power supply.


Q) Is there a full specification or data sheet available for the PiXi (2.0)?

A) Yes, you can download it here.


Q) Can the FPGA be used for Bitcoin mining?

A) This is one of the most common questions we've received. Bitcoin mining is  best suited to much larger FPGAs where there's more memory available. It may be possible to get around 5-10MHash/s with the PiXi (2.0). There is the potential to increate the size of the FPGA by a factor or around four but even this is never going to compete with the Virtex6, Kintex7 boards out there. Perhaps there's a market for a PiXi with a Kintex7 or Zinq... Please do email us if you want to see one and if there's enough interest we'll see about putting something together!


Q) Where are they made?

A) The PiXi (2.0) is (or will be...) made in the U.K.


Q) Can I buy one outside of the U.K.?

A) That’s the plan, we're working to make the PiXi (2.0) available from anywhere in the world.


Q) Is there a user manual available?

A) Please watch this space. We will release the user manual a little later this year.


Q) How is the FPGA programmed?

A) The FPGA is programmed automatically from the on-board SPI flash memory within one second of the power being applied to the board. Alternatively the Raspberry Pi can program both the FPGA & SPI flash directly or a JTAG programming tool such as the Digilent JTAG USB cable can be used to program either the FPGA or SPI flash.


Q) How can the user modify the design of the FPGA?

A) The FPGA can be entirely customised using the example FPGA projects supplied in the start-up pack as a starting point. The Xilinx ISE WebPackTM FPGA design software can be downloaded from the Xilinx website.


Q) Can the PiXi (2.0) use the P5 port on the Raspberry Pi?

A) Yes it can. The connectors that allow it to use this I/O port are not fitted or supplied with the PiXi (2.0) but they can be fitted by the user and the FPGA can be configured to use features available on this interface.


Q) How many serial ports are there?

A) There are two main RS232 level serial ports which can be assigned to the TX/RX serial port on the Raspberry Pi or they can be assigned to one of two UARTS within the default design FPGA. More UARTs can be added to the FPGA and the additional TX/RX interface to these UARTS can be assigned to any of the GPIO ports, either 3.3v or 5v. We've added up to ten internal UARTs so far...


Q) Can the PWM outputs handle digital servos or analogue servos?

A) Yes, in theory. The PWM frequency could easily be set at 50Hz (for analogue servos) or 300Hz (for digital servos). At the moment it's fixed at 50Hz but it's a very minor change to the FPGA design to get them working at 300Hz.


Q) Is the Arduino shield interface 5V or 3.3V?

A) Both. There is a plugable link on the board to allow this to be configured by the user. The link can be configured by connecting a shunt between two points to select 3.3v or 5v.


Q) Is there a low-power mode to preserve battery lifetime when running from a battery?

A) Yes, there are ways that power can be minimised to preserve battery life. This includes low-power / standby modes for some of the on-board components plus a mechanism to intelligently turn the Raspberry Pi on or off.


Q) Are the schematics for the PiXi (2.0) available for download?

A) The schematics will be available for download once the product is released.


Q) How long does it take for the FPGA to configure on power-up?

A) When configured from SPI flash the FPGA will be configured within two seconds of power-up, so the FPGA will be up and running long before the Raspberry Pi has completed its boot sequence. If the Raspberry Pi is being used to configure the FPGA then it can also take around one to two seconds to configure the FPGA once the Raspberry Pi has booted far enough to be able to run the FPGA programming application.


Q) What software gets supplied with the PiXi (2.0)?

A) Each PiXi (2.0) ships with instructions on how to download the software plus a start-up pack from the Astro Designs website. The software pack includes PiXi-Tools - a programming application, library of basic interface functions and some example applications. The start-up pack also includes example FPGA designs.