VHDL code for FPGA bitstream scrubbing for a Xilinx Zynq System on Chip would involve several steps, including:
Defining the VHDL architecture of the scrubbing module, which will include the logic for reading the bitstream, checking for errors, and correcting any errors that are found.
Writing the VHDL code for the scrubbing module, which will include the state machine and the error detection and correction logic.
Integrating the scrubbing module with the rest of the FPGA design, which would include connecting it to the memory controller and any other relevant modules.
Using Xilinx's development tools such as Vivado to synthesize, implement, and download the bitstream to the FPGA.
Verifying the design through testing and simulation to ensure that the bitstream scrubbing is working correctly and that all error scenarios are handled properly.
It's important to note that this is a high-level overview, and the implementation details would depend on the specific requirements and constraints of the system, also it's important to mention that this is a complex task, therefore, it's advisable to consult with experts in the field, and Xilinx official documentation.
Also, it's important to mention that Xilinx provides built-in features for FPGA bitstream scrubbing, such as the Bitstream Scrubber, which could be used instead of developing your own VHDL code for scrubbing.
The Bitstream Scrubber is a built-in feature in Xilinx's FPGA development tools, such as Vivado, that allows for the detection and correction of errors in the bitstream used to configure the FPGA. The Bitstream Scrubber works by reading the bitstream and comparing it to a checksum, which is a calculated value that represents the expected state of the bitstream. If any errors are detected, the Bitstream Scrubber will correct them and re-write the corrected bitstream to the FPGA's configuration memory.
The Bitstream Scrubber can be used in a number of different ways, depending on the requirements of the system. For example, it can be used to periodically check the bitstream for errors and correct them, or it can be used to check the bitstream after a power cycle or other event that may have caused errors in the configuration memory. The Bitstream Scrubber can also be configured to automatically correct errors or to generate an error signal if errors are detected and require manual correction.
The Bitstream Scrubber can be used to check different types of errors, including Single Event Upsets (SEU) that can be caused by cosmic rays and other environmental factors, and manufacturing defects. The Bitstream Scrubber can also be used to detect and correct errors in the configuration memory itself.
It's important to note that the Bitstream Scrubber is a built-in feature in Xilinx's FPGA development tools, it is important to check the documentation provided by Xilinx to see if it's compatible with the specific device used in the design and also check how to configure and enable it in the design.