write data into SRAM on NEXYS4

[whatstartwo]

Hi guys,

   I want to write instruction into nexys4 SRAM to control my small CPU project. What I thought is to use JTAG. But I don't know where to find the USB control interface for nexys4.

   Does anyone could give me a piece of advice on that?

 

Best

Jay.

[JColvin]

Hi Jay,

I know hamster already gave you some feedback on your other post, but here's some more information in case you need it -- if you're just needing to store your program onto the SRAM, you can generate the appropriate bitstream file in ISE or Vivado and then target the CellularRAM (the 'SRAM' that the Nexys 4 has) to store the bitstream. You can use the USB/JTAG interface which is the small micro USB port labeled "Prog" and "UART" on the Nexys 4 board.  The control interface to transfer all of the data transfer from the computer to the Nexys 4 is already taken care of for you so you don't have to worry about it.

Let me know if you have any more questions.

Thanks,
JColvin

[hamster]

Hi JColvin  and whatstartwo,

I'm not sure that what JColvin said is true. 

The Cellular RAM can't be preloaded with data - it is RAM after all and not FLASH. 

So there are at least a couple of options.

1. Include a small bit of block ram in the CPU memory space, and put a bootloader in there. Then load the main program from the SPI flash or over the serial port. All this has to do is read , bytes from the source, then write them into the Cellular RAM and jump to the start of program. This would be the more standard way of doing this.

2. Do much the same as option 1, but using a logic design to do the bootstrapping.See http://papilio.cc/index.php?n=Playground.BombJack for an example on a different board.

3. Load a logic design which populates the memory contents, then reconfigure the FPGA with the desired design.

4. Give your design a JTAG TAP (if that is the correct term), allowing you to take control of it and push data into memory over JTAG.

In my mind, having a bootloader in a block RAM that either configures form serial or SPI flash is way to go.

 

[hamster]

Oh, and if you are interested in how you can append your custom data into a bitstream file, before writing it to the Flash have a look at http://hamsterworks.co.nz/mediawiki/index.php/Config_flash

[JColvin]

I'll defer to hamster as I'm just the Pmod guy. Thank you for the correction.