# Tag Info

2

One case, that probably doesn't apply, is if you're using a standard older than VHDL-2002. Before than, buffer could not connect directly to out. So in a hierarchical design, the signal path would need to be declared as a buffer on all levels. Also, when adhering to these older standards, some tools have problems synthesizing buffers correctly. They may or ...

5

The FPGA configuration itself is stored in SRAM (i.e. flip-flops). A newly started FPGA has an empty configuration where typically all pins are in a somewhat idle state (e.g. weak pull-up), and clocks are not forwarded inside the FPGA, so no activity takes place. From that state, either the FPGA boots actively by accessing an external device (usually, flash ...

1

I know it's a late reply but since I spent my whole day today trying to get this setup to work, I wanted to spare someone else the effort. In short, the digilent tools communicate neither under OSX10.6.8, OSX10.9.4 nor under Win 8.1 -- with virtualbox that is (I used 4.3.14) Turns out that this is a known limitation of virtualbox that persists since 2008. ...

0

Despite being fairly common in the industry to globally cut all paths between two clock groups, I would strongly advise against this practice as it makes it very hard to spot places where you unintentionally re-sampled a signal between clock domains. You are better off using a common block for transferring data between domains. Embed the constraints in the ...

1

Check if jtagd, a deamon between the Altera tools and the driver, is running. If you're running Linux, the QuartusII software changed the way it communicates with the driver around the version change when your problem started. Before they used usbfs, which is no longer the case. You don't state what operating system you are using, but here are a few things ...

1

Yes, the free xc3sprog project ( http://xc3sprog.sourceforge.net ) supports loading Xilinx FPGA firmware through FT232H / FT2232H / FT4232H. This is not officially supported by Xilinx, but does seem to be pretty well supported by the community. The FTDIchip.com USB interface chips FT232H, FT2232H, or FT4232H can be connected to Xilinx JTAG pins as follows: ...

3

Like most FPGA development boards, you can restore the factory shipped configuration by following the same steps you use to load your own firmware, except that the configuration bitstream is ready-made and does not need to be recompiled. So instead of opening and building a project, you instead just go straight into the programming tool. (If this were Xilinx ...

7

The bitstream that controls the functionality of your FPGA is normally called the "configuration", not the "software". The configuration bitstream is generated by using FPGA synthesis tools to compile the Verilog/VHDL source code. There are a number of different ways that the configuration can be transferred into the FPGA each time it "boots up". Roughly, ...

1

Unless the attacker can reprogram the logic, read the flash/eeprom/boot rom or access your programming files on the computer the answer is no. There really is no way to fully determine the switch settings in the layer of cells that contain the configuration setting unless you have direct access to them through the JTAG / programming port. You may be able to ...

0

Looks like it is a problem with Quartus II software. I am using version 13.1, other versions may have this issue resolved. Same question posted here and solved it by configuring the waveform editor to use Quartus II Simulator rather than ModelSim (which is the default).

1

The practical FPGA register (a set of D flip-flops) only has one clock pin so it serves exactly one clock domain. Keep this low-level hardware in mind when writing HDL code. When a signal crosses from one clock domain into another, it's common to use a pipeline of three registers, with the first stage in the source clock domain and the second and third ...

0

The difference between a CPU and FPGA is parallelism. FPGA's are very good at performing a number of (logically) simpler tasks at once with minimal delay. More complex logic and sequences of operations are better catered for by the CPU's ALU (Arithmetic and Logic Unit). If you are interested in a common software emulation of gate design, which is typically ...

1

Other answers have addressed the specific questions at a nuts and bolts detail level, but I think there is an opportunity here to look at it from a different angle. Processors today have many millions (billions in current generation desktop CPUs) of transistors implementing a comparably large number of gates. While only a few of those gates are actually used ...

0

As you have observed, the contents of the lookup table determine whether a certain LUT is an OR gate (0, 1, 1, 1), and AND gate (0, 0, 0, 1), an XOR (0, 1, 1, 0) etc. The lookup table itself is implemented using hardcoded gates, i.e. the result is (lut[0] AND NOT a AND NOT b) OR (lut[1] AND a AND NOT b) OR (lut[2] AND NOT a AND b) OR (lut[3] AND ...

14

Actually your first guess is not as afar off as some are claiming. A CPU is built around something called an "Arithmetic Logic Unit" (ALU) and a simplistic implementation of that is to have the logic gates implementing all basic operations wired up to the inputs in parallel. All of the possible elementary computations are thus performed in parallel, with ...

1

The CPU doesn't just have 'a number' of pre-build logic gates. A modern processor has between around 50 million to several billion transistors, corresponding to many millions of gates. The CPU already has all the resources needed to execute your C++ program. The resources provided fulfill the instruction set defined by that hardware platform, be it x86, ...

7

Pretty far off. A CPU is made up of real gates (not programmable LUTs). The key operations on data are done in a block of logic often known as an ALU (arithmetic-logic unit). Inside this block is a set of gates that can, for example, AND two operands together, bit-by-bit. There's another set of gates that can add them together, and so on. When you execute ...

1

I would use a shift register - use a constant to initialise it to your desired pulse train when reset is asserted and then just clock it out. Your top-level entity will only need three pins, clock, reset and the output.

2

A concurrent signal assignment statement of the form: OUTPUT <= CLK AND VAR; Has an equivalent process (how it's simulated) of the form: process begin OUTPUT <= CLK AND VAR; wait on CLK, VAR; -- wait on 'sensitivity list' end process; With the wait statement the equivalent of putting both right hand side signals in a sensitivity list. ...

10

Yes, it's because you are using the "silicon" oscillator. The basys2 board also provides a socket for a crystal oscillator. If you plug in a crystal oscillator and use its clock signal the jitter is gone and the VGA image will be fine. I have tried it myself. BTW: The manual tells you about that: The primary silicon oscillator is flexible and ...

2

Physical layer Are the 64 GPIOs all you have or do you have any other connections between the FPGAs? As indicated by Martin Thompson, for bandwidth you'd be better off using high speed serial connections if available. Assuming your original post contains all the relevant data and you only have 64 GPIOs then you'll need to think about how you're going to ...

1

As it's Xilinx, you could look at using Aurora to interface between the FPGAs - you'd have to implement your own memory access protocol over the top of it, but it allows you to easily get very high bandwidth between chips using the inbuilt SerDes (GTP) pins. It will handle all the lane matching and channel bonding and save you from the pain of trying to ...

2

You can right click on a warning message, then go to "suppress", then choose between various "quick" suppress options or pop open the Message Suppression Manager that allows you to visualize, edit, import and export all the rules you want. As OP says in the comments below you can also use the * wildcard, so to suppress all pcie messages he wrote *pcie* and ...

1

This absolutely depends on the mouse. I have a USB Microsoft mouse that comes with a similar USB to PS2 adapter. The mouse can sense the difference and reconfigure itself to produce the different protocol but the mouse is marked as such. 99% of the time these adapters are wiring only - there is no intelligence whatsoever within them. Two things to bear in ...

1

You need something like this. However, the device must have a VCO in order for this to work. The circuit works by changing the frequency of a voltage controlled oscillator (VCO) based on the phase difference of two clock signals. The first signal of the two, $F_I$ in the diagram, is the reference signal and in the case of a PLL it is generated by dividing ...

0

There really isn't one answer as there is so many different ways to instantiate a synthesizable design. One way would be to use your synthesizable RTL and resynthesize it with another tool and target a different library. For hand counting, you just need to look at your Mults, FFs and LUTs. The slices are organization hierarchical blocks and taps are ...

2

Implement a DDR controller on FPGA B. Attach the DDR controller to a shared memory interface controller. Attach shared memory interface bus A to FPGA B internals. Attach shared memory interface bus B to FPGA B I/O pins. You may need to make some compromises, of course - 32 bits for data, 31 bits for address, 1 control line probably isn't going to work; ...

1

If you cannot connect the FPGA A to its own bank of memory, then I would venture to say that the 400 MHz GPIO lines between the two are your best bet. Using them in basic SPI configuration or something. If the board is routed properly, you could attempt to do some sort of PCIe communication between the two but that is very circumstantial. You could ...

5

Considering your request a classic serial interface will do the work perfectly. From a HDL perspective a serial transceiver is easy to implement, so I think you should start from here. Your board has no RS232 connectors, but you can easily use the expansion headers in order to connect a FT232 chip, that convert your serial interface to USB. With a ...

2

Yes - you should be debugging in simulation rather than using chipscope on the hardware. For complex designs you will almost certainly save time in the long run by simulating. Xilinx provide some help for simulating PCIe, you should first try and simulate the example designs (see here for Virtex 7 or this Answer Record for 6 series). Since you are ...

3

If you want to do it all in hardware... Good luck. You need to implement the USB standard, or at least a part of it, then find a way to translate whatever your ADC sends in usb packets. If you can integrate a processor in your FPGA that would be so much simpler. With altera you can integrate the nios II processor, so I believe xilinx has its own processor. ...

2

Vivado 2014.1 allows for the usage of .tcl scripts to regenerate projects. To do this, with your project open, go File -> Write Project tcl. Basic Projects I usually store my sources and .tcl script in a location outside of the project directory. The xilinx IP cores generated within the project may be copied elsewhere by right clicking on the core and ...

1

Async FIFOs are characterised by their static latency, expressed as a number of complete cycles in the source domain (before the crossing) and in the destination domain. The crossing itself introduces jitter if there is not an exact phase and frequency relation between the two clocks. In your example you say the phase wanders, for this to happen the clock ...

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