90 lines
4.3 KiB
Markdown
90 lines
4.3 KiB
Markdown
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OpenSBI Firmware with Payload *FW_PAYLOAD*
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==========================================
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OpenSBI **firmware with Payload (FW_PAYLOAD)** is a firmware which directly
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includes the binary for the booting stage to follow the OpenSBI firmware
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execution. Typically, this payload will be a bootloader or an OS kernel.
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A *FW_PAYLOAD* firmware is particularly useful when the booting stage executed
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prior to the OpenSBI firmware is not capable of loading both the OpenSBI
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firmware and the booting stage to follow OpenSBI firmware.
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A *FW_PAYLOAD* firmware is also useful for cases where the booting stage prior
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to the OpenSBI firmware does not pass a *flattened device tree (FDT file)*. In
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such a case, a *FW_PAYLOAD* firmware allows embedding a flattened device tree
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in the .text section of the final firmware.
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Enabling *FW_PAYLOAD* compilation
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---------------------------------
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The *FW_PAYLOAD* firmware can be enabled by any of the following methods:
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1. Specifying `FW_PAYLOAD=y` on the top level `make` command line.
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2. Specifying `FW_PAYLOAD=y` in the target platform *config.mk* configuration
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file.
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The compiled *FW_PAYLOAD* firmware ELF file is named *fw_jump.elf*. Its
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expanded image file is *fw_payload.bin*. Both files are created in the
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platform-specific build directory under the
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*build/platform/<platform_subdir>/firmware* directory.
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Configuration Options
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---------------------
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A *FW_PAYLOAD* firmware is built according to configuration parameters and
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options. These configuration parameters can be defined using either the top
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level `make` command line or the target platform *config.mk* configuration
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file. The parameters currently defined are as follows:
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* **FW_PAYLOAD_OFFSET** - Offset from *FW_TEXT_BASE* where the payload binary
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will be linked in the final *FW_PAYLOAD* firmware binary image. This
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configuration parameter is mandatory if *FW_PAYLOAD_ALIGN* is not defined.
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Compilation errors will result from an incorrect definition of
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*FW_PAYLOAD_OFFSET* or of *FW_PAYLOAD_ALIGN*, or if neither of these
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parameters are defined.
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* **FW_PAYLOAD_ALIGN** - Address alignment constraint where the payload binary
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will be linked after the end of the base firmware binary in the final
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*FW_PAYLOAD* firmware binary image. This configuration parameter is mandatory
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if *FW_PAYLOAD_OFFSET* is not defined. If both *FW_PAYLOAD_OFFSET* and
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*FW_PAYLOAD_ALIGN* are defined, *FW_PAYLOAD_OFFSET* is used and
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*FW_PAYLOAD_ALIGN* is ignored.
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* **FW_PAYLOAD_PATH** - Path to the image file of the next booting stage
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binary. If this option is not provided then a simple test payload is
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automatically generated and used as a payload. This test payload executes
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an infinite `while (1)` loop after printing a message on the platform console.
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* **FW_PAYLOAD_FDT_PATH** - Path to an external flattened device tree binary
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file to be embedded in the *.text* section of the final firmware. If this
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option is not provided and no internal device tree file is specified by the
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platform (c.f. *FW_PAYLOAD_FDT*), then the firmware will expect the FDT to
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be passed as an argument by the prior booting stage.
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* **FW_PAYLOAD_FDT** - Path to an internal flattened device tree binary file
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defined by the platform code. The file name must match the DTB file name
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specified in the platform *objects.mk* file with the *platform-dtb-y* entry.
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This option results in *FW_PAYLOAD_FDT_PATH* to be automatically set.
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Specifying *FW_PAYLOAD_FDT_PATH* on the `make` command line disables
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*FW_PAYLOAD_FDT* and the command line specified device tree binary file is
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used for building the final firmware.
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* **FW_PAYLOAD_FDT_ADDR** - Address where the FDT passed by the prior booting
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stage or specified by the *FW_PAYLOAD_FDT_PATH* parameter and embedded in
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the *.text* section will be placed before executing the next booting stage,
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that is, the payload firmware. If this option is not provided, then the
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firmware will pass the FDT address passed by the previous booting stage
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to the next booting stage.
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*FW_PAYLOAD* Example
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--------------------
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The *[qemu/virt]* platforms illustrate how to configure and use a *FW_PAYLOAD*
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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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The *kendryte/k210* platform also enables a build of a *FW_PAYLOAD* using an
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internally defined device tree file (*FW_PAYLOAD_FDT*).
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[qemu/virt]: ../platform/qemu_virt.md
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