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In a true, embedded application, we will not have a JTAG cable connected that can transfer our programs to the board. Our code must be able to do this before transferring control to an application. Let's return to lab2 and see how we can run our LED dimmer application directly from the SD card or from the on-board SPI flash.
An internal BootROM stores the stage-0 boot code, which configures one of the ARM processors and the necessary peripherals to start fetching the First Stage Bootloader (FSBL) boot code from one of the boot devices. The programmable logic (PL) is not configured by the BootROM. The BootROM is not writable.
The FSBL boot code is typically stored in one of the flash memories, or can be downloaded through JTAG. BootROM code copies the FSBL boot code from the chosen flash memory to On-Chip Memory (OCM). The size of the FSBL loaded into OCM is limited to 192 kilobyte. The full 256 kilobyte is available after the FSBL begins executing.
The FSBL boot code is completely under user control and is referred to as user boot code. This provides us with the flexibility to implement whatever boot code is required for our system.
First stage bootloader
The First Stage Bootloader (FSBL) starts after the boot. The BootROM loads FSBL into the OCM. The FSBL is responsible for:
Initializing with the PS configuration data that Xilinx hardware configuration tools provide
Programming the PL using a bitstream (if provided)
Loading second stage bootloader or bare-metal application code into DDR memory
Handoff to the second stage bootloader or bare-metal application
Create the first stage bootloader
The first step is to create the FSBL application. This is a C program that embeds all the Zynq internal register settings that were established during the Vivado Block Design. We start Xlinx SDK and make sure we have exported the lab2 design from Vivado and that we setup the Board Support Package (BSP).
The SDK program will open with the setup we used in our lab2 experiment. Before creating the FSBL file we have to add a library file used by the FSBL c-program. Select from the top menu:
Xilinx Tools-> Board Support Package Settings
Click OK and wait for the settings window to open.
We will add the xilffs library. We are now ready to generate the FSBL program.
1. Select New->Application Project
2. Enter a name (fsbl_0) and select existing BSP (standalone_bsp_0).
3. Click Next.
4. Select Zynq FSBL and click Finish. When the generation has finished there is a new entry in the Project Explorer namned fsbl_0.
5. Right-click the fsbl_0 entry and select: Build Configurations->Set Active->Release. The release configuration will have less overhead.
6. Build the release configuration by right-clicking and select Build Project.
7. Here is the result:
Generate the boot image
The next step is to create a non-volatile boot image for ZedBoard. The ZedBoard has two non-volatile bootable sources, QSPI flash and SD Card.
1. In the Project Explorer select LED_Dimmer
2. From the top menu select: Xilinx Tools->Create Zynq Boot Image
3. The tool will automatically pick up the files needed to build the boot image.
4. To generate a boot image for the microSD card we will rename the Output path file name (output.bin) to boot.bin and click the Create Image button.
5. To generate a boot image for the SPI flash we will change the Output path file name to LED_Dimmer.mcs and rerun the Create Boot Image generation. It is the file type (bin or mcs) that defines what type of boot image that will be generated.
6. Here is the result.
Boot from the SD card
Copy the boot.bin file to the SD card and insert the card in to the ZedBoard. Set the jumpers to boot from SD card and power up the board. Connect a terminal and control the LEDs by entering different values.
Boot from SPI flash
First we will program the SPI flash using the LED_Dimmer.mcs file we just have generated. To program the SPI flash.