The FAQ on this page represents a list of frequent questions we received after our initial introduction of XLR8. We have recently replicated this information in the FAQ section of our support forums.
If you have a question, please send them our way using the form to the right or ask directly in one of our support forums.
1. Where can I buy an XLR8 board?
XLR8 boards are currently available though Mouser and Arrow Electronics.
2. What FPGA is used on the XLR8 and Snō boards?
It’s an Intel MAX10.
3. What chip is used for the USB to serial interface?
It’s an FT230XQ FTDI chip.
4. Will AloriumTech support users who want to create their own XBs (Xcelerator Blocks) for XLR8?
The short answer is Yes. The long answer is, well, longer… Out of the gate, AloriumTech’s primary goal was to create an FPGA-based board that is a drop-in replacement for the Arduino Uno, meaning that it is the same footprint, runs the same sketches, uses the same libraries, and is programmed with the standard Arduino IDE. The XLR8 board comes pre-loaded with a few different XBs, and supports FPGA image updates via the USB port, which enables users to upload images with new XBs supplied by AloriumTech. There is also a JTAG footprint on the board (which will not be populated on the production boards), so that more advanced FPGA users can use a JTAG programmer (the Intel USB Blaster, specifically) to talk to the FPGA directly. Initially, AloriumTech will provide limited support for users who want to create their own XBs and interface to the on-chip microcontroller. Down the road, we do plan to provide access to enough source code and documentation to make it possible for someone proficient with Verilog or VHDL, and with Quartus, to create their own XBs.
5. What is the price for an XLR8 board?
XLR8 sells for $75 – cost competitive with other high-end Arduino boards.
6. Is there special software required to program an XLR8?
XLR8 uses the standard Arduino IDE for programming. You simply select Uno as your board type, then compile and upload your sketch over USB.
7. How do you tell XLR8 or Snō to use its floating point hardware instead of using lots of clunky Arduino instructions?
In order to access their floating point hardware, we provide a library that you include in your sketch, but there are some changes required to the floating point arithmetic operations in your sketch, as well. Our library defines functions that directly access the general purpose registers within the processor core, such that the hardware-based floating point operations can be performed extremely fast. Any floating point operation that you want to accelerate in your sketch (or in any libraries you’re using) needs to be converted into the XLR8-specific function call. For example:
c = a + b;
c = xlr8FloatAdd(a,b);
Because I’m a lazy typist, I typically do this:
#define xA xlr8FloatAdd
so the line of code I end up with looks like:
c = xA(a,b);
There are similar functions for subtract, multiply, and divide, too. We debated a few different approaches for this, and landed on this one for the time being.
8. Which MAX10 device does XLR8 use? What about larger (or smaller) devices as additional offerings?
9. How much space is available on the FPGA for XBs?
10. Is the microcontroller cycle accurate with a standard ATmega microcontroller?
Yes, based on all of our testing to-date, our implementation of the ATmega-compatible microcontroller is cycle accurate with the standard ATmega micro. If we (or someone else) finds a case where that isn’t true, we are treating that as a bug.
11. Does AloriumTech have plans to develop a dual core or hyperthreaded version of the board?
12. Will AloriumTech also sell the bare FPGA for users who want to build their own board around it?
13. Is it possible to use a toolchain other than the Arduino IDE with XLR8?
14. Is it possible to run the CPU faster than the standard ATmega runs?
15. Does the implementation of the AVR core have the same memory available as the standard ATmega328 part?
The user will see the same program/flash and data/sram memory space as the ATmega328 (32Kbytes and 2Kbytes respectively). Beyond that there is some extra sram on the FPGA that the XBs can use, but that the AVR doesn’t directly see. We don’t have any on-chip EEPROM memory, but the production board design has a spot where an external EEPROM could be added.
16. Will XLR8 and Snō include support for non-AVR cores in the future?
The Arduino ecosystem supports a number of different processor architectures. Because the AVR core seems to be the most prevalent core, and specifically because of its limitations, we wanted to offer an upgrade path to help Arduino users with a large base of AVR code to dramatically improve performance. Down the road, user demand will help us decide on additional upgrades for XLR8 and Snō.
17. Does XLR8 have the same analog I/O capabilities as the Arduino Uno?
18. Is SPI supported on the same pins as on the Uno and the ICSP pins?
Yes it is. There is one note regarding SPI on XLR8 that is worth pointing out from Section 3.9 of the XLR8 User Manual:
The SPI interface on XLR8 should operate the same as the SPI interface on an Uno or Redboard. The only item to note is that we’ve seen some SPI examples where the XLR8/Uno/Redboard is the SPI slave and instead of being driven from the SPI master, the SS pin is left floating. XLR8, due to its I/O pullups, needs to have SS driven and not floating.
19. What is XLR8's digital I/O's voltage capabilities for input and output?
The short answer is that the digital I/O are 5V, both input and output.
The long answer is, well, longer. The FPGA on the board has I/O that support 3.3V for inputs and outputs. On the digital pin input side, we have a FET-based circuit that limits the voltage seen by the chip to about 3.3V, so the inputs would correctly be categorized as 5V-tolerant. On the digital pin output side, again the chip is a 3.3V device, so it only drives to 3.3V. We have a 1K-ohm pull-up resistor on the board that pulls the signals up to 5V at the board interface, so what you’ll see at the board level is true 0-5V signalling.
The analog pins are a bit different. Those can also be configured as digital I/O on an Arduino, and the same is true on XLR8. There is a slightly more complex circuit to manage the inputs, since we want to be able to have the 3.3V ADC on the chip work over a 0-5V analog voltage range. The net is that, when used as digital inputs, those pins are also 5V-tolerant. However, we don’t have the pull-up resistors on those pins, so when configured as digital outputs, they will drive from 0 to 3.3V, and not to 5V.
20. What is the best method and components to mate the Snō connections to the SnōMākr connections?
The cleanest way (but probably the most challenging) is to solder the Snō board directly to the SnōMākr with no headers at all. If you line up the Snō to the SnōMākr, it’s possible to flow solder through the vias of both boards simultaneously and create a direct connection between the boards. As I mentioned, this is a bit challenging to do, and it also would make it very difficult to separate the boards if you wanted to in the future.
Another approach that is still very clean and compact is to use pin headers as the interface between the boards. We often use something like this:
You’ll need a couple of those, since there are 59 connections between the boards. Soldering is much easier, and you still end up with a very clean solution. Future disassembly will also be challenging with this solution.
Finally, you could use headers on the SnōMākr board, and pins on the Snō to create a plug-in solution. We’ve used these:
This creates a very clean, low-profile solution that allows shields to still be used with the SnōMākr, and allows the Snō board to be removed if needed.
As far as a sequence, it comes down to accessibility of the pins with the soldering iron. You’ll want to use a small tip on the iron, and in general start with pins toward the center of the board and work your way out. If you’re soldering the boards together with no headers (again, the most challenging option listed above!), you’ll want to be very careful to avoid melting the SnōMākr headers as you’re reaching between them to solder.