pynq_to_zynq

Loopback Project Step 5: Advanced Workflows

1. The Goal

To evolve our prototype into a professional-grade embedded system. We will learn to:

1. Hot-Swap Hardware: Update the FPGA logic on a running system without rebooting.
2. Bake Applications: Integrate our C code into the SD card image as a system utility.
3. Enable Self-Hosting: Install gcc and build tools on the board for rapid on-device iteration.

2. Sanity Check

• Step 4 Complete: You have a working PetaLinux build and have verified the loopback_test application works manually.
• PetaLinux Tools: Source the settings script (source /tools/Xilinx/PetaLinux/2025.1/settings.sh).

3. Topic A: Dynamic Hardware Updates (The Hot-Swap)

Imagine you found a bug in your Verilog (or you just want to change the adder to +5). You do not need to rebuild the whole OS or reboot the board to test this.

Step 1: Modify & Regenerate

1. Vivado: Open your IP Source (math_accelerator_v1_0_S00_AXI.v).
2. Edit: Change the logic from + 32’d1 to + 32’d5.
3. Repackage: Re-package the IP (as done in Step 1).
4. Bitstream: In the main project, click Generate Bitstream.
   • Result: You get a new system_design_wrapper.bit.

Step 2: Convert Bitstream to Binary

Linux cannot load a .bit file directly because it contains a text header. We must strip it using the Xilinx bootgen tool (available in your shell after sourcing settings).

1. Locate Bitstream:
   Find your generated .bit file (usually in <vivado_project>/<project>.runs/impl_1/).
2. Create BIF File:
   Create a text file named bitstream.bif with this content:

   all:  
   {  
       system_design_wrapper.bit  
   }
   

3. Run Bootgen:

   bootgen -image bitstream.bif -arch zynq -process_bitstream bin
   

   • Result: You now have system_design_wrapper.bit.bin.

Step 3: Hot-Swap

1. Transfer: SCP the .bin file to the board.

   scp system_design_wrapper.bit.bin petalinux@<BOARD_IP>:/home/petalinux/
   

2. Load: On the board, use the Xilinx FPGA Utility.

   sudo fpgautil -b system_design_wrapper.bit.bin
   

   • Note: You might see a warning about “Timeouts” or “Flags”. Usually, it succeeds.
3. Verify: Run your loopback_test app.
   • Success: It should now report Read 47 (if input was 42 and logic is +5).

4. Topic B: Baking the App (Yocto Recipes)

Copying the C binary manually is tedious. Let’s make PetaLinux compile and install it automatically every time we build the OS.

Step 1: Create the App Recipe

In your PetaLinux project folder:

petalinux-create -t apps --name loopback-test --enable

• This creates a folder structure at project-spec/meta-user/recipes-apps/loopback-test/.

Step 2: Update Source Code

1. Navigate to project-spec/meta-user/recipes-apps/loopback-test/files/.
2. Delete the auto-generated loopback-test.c.
3. Copy your working loopback_test.c (from Step 4) into this folder.
4. Rename it to loopback-test.c (to match the Makefile generated by PetaLinux).

Step 3: Build & Deploy

1. Rebuild:

   petalinux-build
   

   • Note: This will be much faster than the first build because it only compiles your app and repackages the rootfs.
2. Package:

   petalinux-package --wic --bootfiles "BOOT.BIN image.ub boot.scr" --rootfs-file images/linux/rootfs.tar.gz
   

3. Result: When you boot this new image, you can simply type loopback-test at the prompt. It is installed in /usr/bin/ automatically.

5. Topic C: On-Board GCC (Self-Hosting)

For rapid testing, you might want to compile code directly on the Zynq, just like on a Raspberry Pi.

Step 1: Configure RootFS

1. Open the configuration menu:

   petalinux-config -c rootfs
   

2. Navigate to Petalinux Package Groups.
3. Select packagegroup-petalinux-self-hosted.
   • What this does: It selects gcc, make, binutils, glibc-dev, and other build tools.
4. Exit and Save.

Step 2: Rebuild

1. Build:

   petalinux-build
   

   • Warning: Your rootfs size will grow significantly (by 100MB+). Ensure your SD card partitions are large enough.
2. Package (WIC):

   petalinux-package --wic --bootfiles "BOOT.BIN image.ub boot.scr" --rootfs-file images/linux/rootfs.tar.gz
   

3. Flash: Flash the new petalinux-sdimage.wic to your SD card (just like in Step 3).

Step 3: Verify

1. Boot the new image.
2. On the board, check the compiler:

   gcc --version
   

3. Workflow Upgrade: You can now edit C files on the board using vi or nano and compile them immediately with gcc loopback_test.c -o test, skipping the cross-compilation step entirely.

6. Recap

You have moved beyond “getting it to work” to “working efficiently.”

• Hot-Swapping lets you iterate on Hardware logic in seconds.
• Recipes let you productize your Software so it survives reboots and distribution.
• Self-Hosting gives you a powerful on-board dev environment for debugging.

You now possess the complete toolkit of a Zynq Full-Stack Developer.

7. Next Step

We have a professional workflow, but a minimal OS. Let’s upgrade to a full Desktop experience.

Go to Step 6: The Debian Hybrid

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