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Field programmable gate arrays (FPGAs) are extremely powerful, but until recently, programming them has been an obscure art. Now, thankfully, it has been made much simpler and easier due to the availability of beginner-friendly development boards and free, opensource graphical programming software. We explore what you can do with the lowcost and compact iCEstick board, and free IceStudio software. Part 1 Introduction to programming FPGAs iCEstick F or a long time, programming and developing FPGAs has been difficult, especially for the hobbyist who doesn’t have access to the often expensive tools that are needed. On top of this, understanding the language that is used to describe a design can be a challenge, as is getting one’s head around the ways FPGAs work differently to microcontrollers. The iCEstick development board from Lattice Semiconductor (a major FPGA IC manufacturer) is a compact unit which plugs into a USB port. Thus the board and programming hardware are one and the same, requiring only the extra components for a particular application to be added on. Even this is not always necessary, as the board sports five LEDs which can be controlled by I/O pins, plus an onboard infrared transceiver. The code for the iCEstick can be generated using Lattice iCEcube development software, available with a free licence. The Diamond programmer software is then used to program the iCEstick with the resulting file. 26 We also tried an open-source alternative called IceStudio. It has a graphical interface, allowing logic blocks to be dragged and dropped, then connected by virtual wires to create a representation of the circuit to be synthesised. It is a complete IDE, allowing design, building and uploading to occur. For users who are comfortable with how logic gates and other basic elements like flip-flops work, this is an ideal way to bridge the gap of understanding between having an idea in one’s mind and turning it into a functioning circuit. IceStudio also allows ‘code blocks’ containing Verilog code to be created, so those who are familiar with Verilog are not limited by the included graphical symbols. Verilog is a bit like the C language, as used to program an Arduino, but is designed to produce logic block structures rather than machine code. by Tim Blythman What is an FPGA? FPGA stands for ‘field programmable gate array’, and this means that it consists of logic gates, flip-flops and other ‘glue’ logic which can be (re-)configured to perform different functions. While this is an over-simplification, you can think of an FPGA as an IC containing thousands of 4000B/74HC/74LS chips connected via crossbars; in effect allowing you to change how the inputs and outputs of those devices are connected, to form virtually any function. And since they are all inside the same chip, very high speeds are possible; up to 500-1000MHz in some parts. The advantage that this arrangement has over a microcontroller is that everything happens at the same time in an FPGA. Rather than having to wait for things to process in a sequence, determined by the list of instructions which form the program, everything happens practically instantly in an FPGA. This makes them ideal for tasks where many different calculations can be made in parallel. While some Practical Electronics | April | 2020 Table1: iCEstick physical pin to I/O pin mapping The iCEstick, slightly under life size. The huge (144-pin TQFP) IC in the middle of the iCEstick is the iCE40HX-1k. To the right of it are the various I/O headers and five user LEDs. To the left are the flash and EEPROM ICs, an FTDI 2232H dual UART and a 12MHz oscillator. microcontroller processors do have multiple cores, allowing several instructions to be executed simultaneously, in an FPGA, practically everything happens simultaneously. So it’s a bit like having a processor with thousands (or even millions) of cores; even though each of those cores may have fairly limited capabilities, the overall result is a much more powerful and capable device. A good example of a digital task which is quite easy to do with an FPGA but virtually impossible with a regular microcontroller, as demonstrated by the Arduino MKR Vidor 4000, is the generation of an HDMI digital video signal. The FPGA can produce the HMDI data (which is typically clocked at hundreds of megahertz) far quicker than any microcontroller could possibly manage. And it can do this while performing whatever other tasks are required simultaneously, without any concerns that the different tasks may interfere with the time-critical video generation process. Rather than software code (eg, BASIC, C, assembly language), the FPGA configuration is described in a hardware description language (HDL). There are two main HDLs in widespread use: Verilog and VHDL. We will mostly be dealing with Verilog, which borrows some of its syntax from the C language; but due to the nature of FPGAs, it has some important and significant differences. The HDL is synthesised into a ‘bitstream’ (basically, a blob of binary data), which is what is actually loaded into the FPGA chip to configure it. In the case of the iCE40HX-1k FPGA on the iCEstick, this is up to 34kB in size. The bitstream is roughly the equivalent of machine code to a microcontroller or microprocessor. There is a lot more to this process than this simple description suggests, and much of how FPGAs and FPGA development tools work has been hidden by the manufacturers until the advent of the open source tools we are now using. Practical Electronics | April | 2020 Pin Function 21 12MHz Osc. 8 UART TX 9 UART RX 78 PMOD 1 79 PMOD 2 80 PMOD 3 81 PMOD 4 87 PMOD 7 88 PMOD 8 ICE40HX chip and iCEstick board capabilities While touted as having a USB thumb drive form factor, it actually measures 95 × 25mm. But when you consider that a large portion of this board is taken up by the sizeable FPGA chip, its size seems reasonable. This IC is a Lattice iCE40HX-1k FPGA which comes in a 144-lead TQFP package. While not all the input/output pins are broken out (the chip has 96 I/O pins in total), an ample number are available. The iCE40HX-1k contains 1280 flipflops, 1280 lookup tables, 160 programmable logic blocks and 16 RAM blocks. Each RAM block holds four kilobits (512 bytes), for a total of 8 kilobytes. For comparison, its larger sibling, the iCE40HX-8k, can emulate a 32-bit RISC processor, but this is a bit beyond the iCE40HX-1k’s capabilities. The core of the chip runs at 1.2V, but external I/O on the iCEstick is 3.3V. There are four I/O banks on the iCE40HX-1k which can (in a different implementation) be set to other I/O voltages. Also on the iCEstick board are several other components for communications and programming. The second-largest IC, nearest the USB plug, provides the USB interface. This is an FTDI 2232H dual UART with USB 2.0 Hi-Speed. Typically, one of the UARTs is used in SPI mode for programming, and the second UART is Pin Function 90 PMOD 9 91 PMOD 10 95 LED5 (GREEN) 96 LED4 (RED) 97 LED3 (RED) 98 LED2 (RED) 99 LED1 (RED) 105 IR TX 106 IR RX available for communication with the bitstream that is ‘running’ on the FPGA. The two 8-pin SOIC devices are a Flash IC and an EEPROM IC. The Flash IC is 32Mbit and is used to store the configuration bitstream in a nonvolatile fashion. The FPGA is configured using internal RAM, the contents of which is lost on power-down, so it must be loaded from the Flash chip each time power is applied. While the FPGA has the facility to load its configuration from its own internal non-volatile configuration memory, this memory can only be programmed once, so a reprogrammable Flash chip is used until a design is finalised. The EEPROM is simply used to hold the configuration for the FTDI 2232H and the remaining IC is an LT3030 dual low-dropout linear regulator. There is also a 12MHz clock source on the iCEstick. This clock source is necessary for all but the most basic logic designs. The iCE40HX-1k also features a PLL, so designs are not limited to 12MHz, as higher frequencies can be generated by the PLL from the 12MHz source. On the far side of the FPGA are the I/O breakout headers. Five LEDs (marked D1-D5) are arranged in a diamond pattern, flanked by two 0.1inch pitch 10-pin breakouts. Each of these provides eight I/O pins plus ground and 3.3V power. Screen1: ensure that the correct device is selected in the Zadig application, and that libusbK is selected before clicking ‘Replace’ and closing the window. If you do change the wrong driver, you can uninstall it via device manager. 27 Screen3: if you need to remove IceStudio’s drivers to allow the Diamond Programmer to work with the iCEstick then find this entry in Device Manager, right-click it and choose Uninstall Device. Unplug and replug the iCEstick and Windows should reinstall the default drivers. Screen2: IceStudio’s ‘Two LEDs alternate blink’ example (which they incorrectly refer to as ‘alternative’). The small yellow box at left represents the 12MHz crystal clock on the iCEstick. It is followed by a 22-stage binary divider, effectively dividing the 12MHz clock by a factor of 4,194,304 (ie, by 222, to around 3Hz). Digital pins D1 and D2 are connected to two LEDs on the iCEstick board, and are driven with square waves derived from the 3Hz clock, one directly, and one via a NOT gate so that it is on while the other is off. The 6×2 female header block matches Digilent’s PMOD interface, and provides eight more I/Os, plus ground and power. Finally, at the end of the board opposite the USB connector is an IR transceiver chip, which is connected to another two of the FPGA’s I/O pins. This gives 24 unallocated I/O pins available for use, plus at least ten dedicated to I/O functions on the board itself. Other FPGA boards After acquiring the iCEstick, we looked around for other FPGA development boards; in particular, those supported by IceStudio. Many of these are open-sourced hardware designs that are being promoted on crowd-funded websites. In general, we found that most of them were more expensive than the iCEstick. A few were cheaper, but also required a separate programmer. So for this reason, and because the iCEstick is easy to buy, we decided to stick with it. The fact that two different software packages can be used to program it is also a plus. Software for the iCEstick In the following discussion of the software options, we will only give very basic examples. If you want something more involved (and useful), see our iCEstick VGA Terminal project, which we will cover next month. There, we’ll delve much deeper into what can be done with the iCEstick and IceStudio. IceStudio software The open-source IceStudio software is a free download. We found it straightforward to use, and had 28 a working project uploaded to the board in minutes. There are example projects available which appear quite basic, but they are all great building blocks. The version we tried was just over 100MB, although you also need to download some other required software packages, such as the ‘toolchain’. Installing IceStudio IceStudio can be downloaded from its Github page at https://github.com/ FPGAwars/icestudio Like many open source tools, it’s available for Windows, Linux and macOS. We used the v0.4.0 release. Although this release number indicates it is still in beta, we found the software to be mature and didn’t run into many bugs. Behind the scenes, it uses the open-source IceStorm project to synthesise the bitstream alongside some configuration files, but you don’t need to concern yourself with these details while using IceStudio. In this regard, it is similar to Arduino, which uses the open source gcc compiler and the AVRDUDE programming tool to provide most of its functions, with inbuilt board configuration files. This means the user does not have to worry about the minute details of the specific hardware used. Installing IceStudio was quite straightforward. About halfway down the Github page (link above), there is an installation guide, with brief, simple instructions for Linux, Windows and macOS, with links to the downloads. We installed on Windows 10, so some of the steps below may not apply to Linux or macOS; in particular, the driv- er switching step is probably not needed on these other operating systems. The installer does not automatically install the required toolchain – you will be prompted to install it when the program first runs. No further input is required apart from confirming that installation should proceed. IceStudio also includes a bitstream programmer, but this does not work with the default device driver for the iCEstick under Windows. Again, a simple tool allows the appropriate driver to be installed and uninstalled (which is necessary if you wish to also use Lattice’s iCEcube software). The driver switcher uses the Zadig driver utility. IceStudio gives you some prompts which explain how to use Zadig, then opens the program, allows you to make the changes, and then prompts you to unplug and replug the iCEstick. This is all fairly seamless, and it’s comforting that the program is upfront about what changes you are making. The Zadig utility also has the option of changing other drivers, so great care should be taken that you don’t inadvertently change the wrong driver. We also noticed that, very occasionally, Windows would reload the old driver (perhaps when the iCEstick was plugged into a different USB port). In that case, it is merely necessary to rerun the driver switcher routine. Setup Once the installer has finished, start IceStudio. You will be prompted to install the toolchain, which requires the Python scripting language to be installed, plus a few other packages. If you are not prompted, check the Tools → Toolchain menu, and click Update if you are unsure. We found that this proceeded without any problems, although you need Internet access to download these extra packages. You will then be prompted to update the drivers. This is only possible if you have an iCEstick connected. Practical Electronics | April | 2020 Screen4: this screen grab shows the iCEcube2 new project settings to suit the iCEstick. The project name and location can be set to suit your system, but the device properties are critical for correct operation. If you don’t have an iCEstick, skip this step. Again, there is no harm in checking the drivers if you are not prompted. Now click Tools → Drivers → Enable. IceStudio will indicate a few steps that will occur. Click OK to proceed. Note the message about using USB 2.0 ports. We ran into problems using the iCEstick on a USB 3.0 port, but were able to use a USB 2.0 hub to ‘downgrade’ our connection to USB 2.0 and it worked after that. When the Zadig Driver Utility opens (Windows may ask for permission for the program to make changes), take great care to change the correct drivers. Zadig has facilities for many drivers, but we only want to change those for the iCEstick. Ensure that ‘Lattice FTUSB Interface Cable (Interface 0)’ is selected in the dropdown and check that the item to the right of the green arrow is ‘libusbK’ (in our case, version 3.0.7.0), then click ‘replace driver’ (see Screen1). IceStudio will now prompt you to unplug and replug the iCEstick. Do this to ensure that the drivers are loaded correctly. The final step is to select the development board. This is done from the Select → Board menu; the iCEstick is found under the HX1K subheading. Selecting the correct board means that friendly names are availPractical Electronics | April | 2020 able for the various I/O pins. For example, a pin named ‘D1’ can be selected, which maps directly to LED1 on the iCEstick. This completes the setup. There are examples available under the File → Examples menu. Many of these appear to be written for other boards, but are simple enough to adapt for the iCEstick. The only real differences appear to be the I/O pin mappings, which are blanked on conversion. We also suggest enabling the FPGA resources view, by clicking View → FPGA resources, and ensuring this item is ticked. The bottom bar of the window will now show the resource usage, which is empty at this stage. This will let you keep track of how ‘full’ your FPGA is. Using IceStudio A good place to start is the example available under the following menu: File → Examples → Basic → Two LEDs alternate blink. Upon opening this, you will be prompted that it is designed for a different board; simply click ‘convert’. As mentioned above, conversion involves removing any I/O pins associated with the old board. To complete the conversion, click on the LED dropdown boxes, and select D1 and D2 (see Screen2). The next step is to compile the project into a bitstream. Click Tools → Build or press Ctrl-B. After a few seconds, a message will pop up which should say: ‘Build done’. Finally, click Tools → Upload to send it to the iCEstick. The LEDs will all light up dimly during the upload stage, and if the upload is successful, two of the LEDs should be alternately flashing. If you have trouble with the upload, check the drivers using the Enable Driver option or try a different USB port. We recommend looking at the examples to see what can be done with IceStudio. The four menu items at top right are various items that can be dropped into the editor to create your project. Included in these (under Basic) is a ‘Code’ option. This allows blocks containing Verilog code to be included. For those familiar with Verilog, the blocks are effectively the same as Verilog modules. Such a code block can even be exported and used in another project. You can build just about any set of logic using Verilog, including adders, accumulators, multipliers, dividers, multiplexers, memories, register files and so on. The various gates and other blocks can be joined by wires. To create a wire, move the mouse to an output pin of a block until the pointer becomes a black cross. Click, and drag the wire to the input of another block and release. We found the wires to be one of the fiddliest parts of IceStudio. They can only be dragged from output to input, and often end up in awkward places. They can be dragged to neaten the layout or removed by hovering over the wire, and then finding the small red ‘x’ and clicking on it. The software has all the usual editing facilities such as copy, paste and undo, and they all work rather well once you get used to it. You can press and hold the right mouse button to pan around the window, and the scroll wheel on the mouse allows zooming in and out. A full user guide is available at: https://icestudio.readthedocs.io/en/latest/ Note that if you have used IceStudio to enable its driver, you will need to disable it to allow the Diamond Programmer to use its driver. The Tools → Drivers → Disable menu is a bit cryptic about this. What you need to do is open Device Manager, find the libusbK driver entry, right click on it and uninstall it (Screen3). Then unplug and replug the iCEstick, and Windows will reinstall the default drivers. This isn’t necessary on macOS or 29 Screen5: the iCEcube window after our project has been converted into a bitstream. Despite all the red text, everything completed without errors. The Pin Constraints Editor is the icon below the left of the Window menu. Linux, as the same drivers are used for both software packages. iCEcube2 iCEcube2 is proprietary software, and while you can freely download it and install it, a license key is needed to run it. This is all available at no cost, but you will need to create an account on the Lattice website to receive a license key. We found the process of setting up an account and requesting a key a bit slow, but it worked, and we got our key in the end. The key is tied to a specific Ethernet MAC address, meaning you will need multiple licenses if you want to run the software on multiple computers. The iCEcube2 version we downloaded was around 750MB, and a separate download of the ‘Diamond’ programmer application is needed too. There are versions of iCEcube2 available for Windows and Linux; download from: http://bit.ly/pe-apr20-ice1 The separate programmer software is found at: http://bit.ly/pe-apr20-ice2 Ensure that you have the license file for iCEcube2. There is a link on the information page for iCEcube2 detailing how to receive the license file via email. Although the email notes that the license file should be placed in the \license directory of our install, there did not appear to be such a directory. Our install of iCEcube2 has the path C:\lscc\iCEcube2.2017.08, so we placed a copy of the license in both the lscc and iCEcube2.2017.08 directories, and everything seemed to work, although it did sometimes complain that the license file was missing. We struggled to find simple examples that would work for the iCEstick under iCEcube2, and certainly didn’t find any on Lattice’s website. In the end, we found a basic ‘blink’ exam30 ple at: http://bit.ly/pe-apr20-ice3 but even this missed one or two steps, so we had to modify it. ICEcube2 uses VHDL, so if you prefer VHDL over Verilog, this may be an option, although VHDL is generally stricter and more verbose than Verilog (Editor’s note: in my opinion, Verilog is superior, although they both have roughly the same capabilities). To use iCEcube2, first create a new project, and fill in the details as shown in the screen grab (Screen4), to match the hardware of the iCEstick. Click OK, and the ‘add files’ dialog box opens; click ‘Finish’, as files can be added from within the project. You can download the BLINK.vhdl file from the April 2020 page of the PE website. Copy this file to within the project folder, then add it to the project by right-clicking on ‘Add Synthesis Files’. Select the file and then press the ‘>>’ button to add it to the project. The ‘Run Synplify Pro Synthesis’ button is the first step in turning the project into a bitstream. Double-click this, and check that there are no errors. We got an error message about the license file, but it worked anyway. Next click ‘Import P&R Input Files’. You should see a pattern of working through several steps along the lefthand side of the project window, with the green triangles turning into ticks as the steps are completed by doubleclicking on them (see Screen5). After the P&R (place and route) files have been imported, the pins need to be assigned. This is done with the Pin Constraints Editor, selected from the row of icons below the menus. In our version, it is the fourth icon, which looks like a blue square with pins coming out of it. The physical pin to I/O pin mapping is shown in Table 1. LED1 and LED2 should be set to pins 95 and 96 (or any of the other LED pins from the table), and ‘clk’ (the clock signal input) should be set to pin 21. Save the project to register the new pin assignments. Finally, in turn, double click ‘Run Placer’, ‘Run Router’ and ‘Generate Bitmap’. The generated bitmap is the file that will be loaded onto the iCEstick. It can be found buried within the project folder; eg, \BLINK_Implmnt\sbt\ outputs\bitmap\BLINK_bitmap.bin Diamond Programmer Now we use the Diamond Programmer application to load the bitstream onto the iCEstick. Open Diamond Programmer, select ‘Create a new blank project’ and click OK. Under ‘Cable Settings’ to the right, click ‘Detect Cable’; the selected cable should include FTDI in its name. We found we had to set the port to FTUSB-1 (see Screen6). In the main window, set the device family to iCE40 and the device to iCE- Screen6: the Diamond Programmer window. Check the Device, Device family and Cable settings to ensure they are correct. The Device Properties icon is immediately below the Help menu item, while the Program button is the one with the large green arrow. Practical Electronics | April | 2020 40HX1K. Under File Name, browse to the bitmap file created by iCEcube2 and select it. Click the ‘Device Properties’ icon (a chip with a small yellow pencil) and set that as shown in the screen grab (Screen7). Finally, you click the ‘Program’ button to transfer the bitstream to the iCEstick. If all is well, your Output Window at bottom left should look like our screenshot, and you should see two LEDs flashing alternately on the iCEstick. Conclusion We devoted more space to describing the iCEcube2 and Diamond Programmer software than IceStudio because it requires more work to achieve the same result. We found that IceStudio was a real pleasure to use and would highly recommend it to anyone who has not worked with FPGAs before. We found a couple of small glitches, including occasional crashes even on quite small projects. So save your work often. We also found IceStudio became quite sluggish on larger projects, taking some time to zoom and move around. We imagine that as we become more proficient with Verilog, that our IceStudio projects will consist of nothing more than a single large code block, which should not present the same performance issues as lots of smaller blocks. IceStudio also appears to have the benefit of being written specifically for development boards such as iCEstick. If you are a professional developer, especially someone looking to build an FPGA into an end product, the flexibility and complexity of iCEcube2 will be warranted. Just choosing a different Flash IC to that fitted or another small hardware change different to the iCEstick would probably be enough to hamper IceStudio in these cases. With iCEcube2, once we had our project set up, everything worked quite well; similarly, Diamond Programmer worked quite well, although the time spent pulling hair and debugging cryptic error messages was quite a bit more than we had hoped. But for someone who has not worked with FPGAs before, IceStudio will give a smooth, easy way for you to become accustomed to what is possible. Hardware In terms of hardware, there are a few development boards around which feature more powerful FPGAs than the iCEstick discussed here. However, for now, the iCEstick suits our purposes, and we think it will be a great starting point for those wishing to try out FPGAs for the first time. It is available from Mouser and Digikey for around £20. Next month Finally, just a reminder that next month in Part 2 we’ll put FPGA theory into practice by building an iCEstick VGA Terminal. www.poscope.com/epe - USB - Ethernet - Web server - Modbus - CNC (Mach3/4) - IO - PWM - Encoders - LCD - Analog inputs - Compact PLC Reproduced by arrangement with SILICON CHIP magazine 2020. www.siliconchip.com.au Screen7: we’d never have guessed these properties, so we’re glad we found a guide to help us out. Make sure you don’t select NVCM programming. That is the nonerasable (write-once) memory built into the iCE40HX-1k IC. We use the Flash memory instead, to allow repeated write/ erase cycles. - up to 256 - up to 32 microsteps microsteps - 50 V / 6 A - 30 V / 2.5 A - USB configuration - Isolated PoScope Mega1+ PoScope Mega50 - up to 50MS/s - resolution up to 12bit - Lowest power consumption - Smallest and lightest - 7 in 1: Oscilloscope, FFT, X/Y, Recorder, Logic Analyzer, Protocol decoder, Signal generator Practical Electronics | April | 2020 31