Bitstream for Zybo Z7-20 Petalinux BSP Project

[DigbyT]

I have gone through the Digilent Zybo Z7-20 Petalinux BSP Project here:

https://github.com/Digilent/Petalinux-Zybo-Z7-20/releases/tag/v2017.4-3

And have used it to successfully build the project, including with modificatons described to create a SD based system with full development system based on a Ubuntu userland. 

There is only one mystery I have so far never solved - the file package includes a bitstream in images/linux/system_wrapper.bit which is included in all the example "petalinux-package" commands, but I have no idea where this bitstream came from or what functionality it might define. I assume that the '--fpga' argument can be omitted if no bitstream is required, so I have assumed this must be being included for a reason. When booting the Petalinux image from SD, I don't see any of the LED activity that is visible when running Q-SPI based demo.

Can anyone elaborate on what the story is behind this bitstream? Can I safely replace it with something else? Or just omit it completely?

Thanks,

DigbyT

[JColvin]

Hi @DigbyT,

I believe the bitstream comes from the Base Linux project on our GitHub: https://github.com/Digilent/Zybo-Z7-20-base-linux and is used as the source to configure the FPGA after it has booted up (since the FPGA itself is volatile, unlike QSPI or the SD card).

@Ionel would be better able to clarify the details on this.

Thanks,
JColvin

[Ionel]

@DigbyT,

The bitstream is for the PL component in zynq. Option --fpga is used to provide a custom bitstream in case you have a different hardware description(hdf|xsa) than the one used to configure the petalinux project. The bootloader is responsible to load the PL(FPGA) with the provided bitstream.
If you omit the --fpga option then `images/linux/system.bit` will be used by default.
Replacing the bitstream is like changing parts of the hardware, it may  be safe but only if the software is ready/prepared the handle those changes. In some cases the device tree also need to change.