52 lines
2.2 KiB
Markdown
52 lines
2.2 KiB
Markdown
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OpenSBI Firmware with Jump Address *FW_JUMP*
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============================================
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OpenSBI **firmware with Jump Address (FW_JUMP)** is a firmware which only
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handles the address of the next booting stage entry, e.g. a bootloader or an OS
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kernel, without directly including the binary code for this next stage.
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A *FW_JUMP* firmware is particularly useful when the booting stage executed
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prior to the OpenSBI firmware is capable of loading both the OpenSBI firmware
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and the booting stage binary to follow the OpenSBI firmware.
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*FW_JUMP* Compilation
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---------------------
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A platform *FW_JUMP* firmware can be enabled by any of the following methods:
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1. Specifying `FW_JUMP=y` on the top level `make` command line.
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2. Specifying `FW_JUMP=y` in the target platform *config.mk* configuration file.
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The compiled *FW_JUMP* firmware ELF file is named *fw_jump.elf*. Its expanded
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image file is *fw_jump.bin*. Both files are created in the platform-specific
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build directory under the *build/platform/<platform_subdir>/firmware* directory.
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*FW_JUMP* Firmware Configuration Options
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----------------------------------------
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To operate correctly, a *FW_JUMP* firmware requires some configuration
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parameters to be defined using either the top level `make` command line or the
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target platform *config.mk* configuration file. The possible parameters are as
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follows:
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* **FW_JUMP_ADDR** - Address of the entry point of the booting stage to be
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executed following OpenSBI firmware. This address generally corresponds
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exactly to the address where this next booting stage was loaded. This is a
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mandatory parameter. Compilation errors will result from not defining this
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address.
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* **FW_JUMP_FDT_ADDR** - Address where the *flattened device tree (FDT file)*
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passed by the prior booting stage will be placed in memory before executing
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the booting stage following the OpenSBI firmware. If this option is not
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provided, then the OpenSBI firmware will pass the FDT address passed by the
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previous booting stage to the next booting stage.
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*FW_JUMP* Example
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-----------------
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The *[qemu/virt]* platform illustrates how to configure and use a *FW_JUMP*
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firmware. Detailed information regarding these platforms can be found in the
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platform documentation files.
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[qemu/virt]: ../platform/qemu_virt.md
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