OpenSBI Firmware with Payload (FW_PAYLOAD) ========================================== OpenSBI **firmware with Payload (FW_PAYLOAD)** is a firmware which directly includes the binary for the booting stage to follow the OpenSBI firmware execution. Typically, this payload will be a bootloader or an OS kernel. A *FW_PAYLOAD* firmware is particularly useful when the booting stage executed prior to the OpenSBI firmware is not capable of loading both the OpenSBI firmware and the booting stage to follow OpenSBI firmware. A *FW_PAYLOAD* firmware is also useful for cases where the booting stage prior to the OpenSBI firmware does not pass a *flattened device tree (FDT file)*. In such a case, a *FW_PAYLOAD* firmware allows embedding a flattened device tree in the .text section of the final firmware. Enabling *FW_PAYLOAD* compilation --------------------------------- The *FW_PAYLOAD* firmware can be enabled by any of the following methods: 1. Specifying `FW_PAYLOAD=y` on the top level `make` command line. 2. Specifying `FW_PAYLOAD=y` in the target platform *config.mk* configuration file. The compiled *FW_PAYLOAD* firmware ELF file is named *fw_jump.elf*. Its expanded image file is *fw_payload.bin*. Both files are created in the platform-specific build directory under the *build/platform//firmware* directory. Configuration Options --------------------- A *FW_PAYLOAD* firmware is built according to configuration parameters and options. These configuration parameters can be defined using either the top level `make` command line or the target platform *config.mk* configuration file. The parameters currently defined are as follows: * **FW_PAYLOAD_OFFSET** - Offset from *FW_TEXT_BASE* where the payload binary will be linked in the final *FW_PAYLOAD* firmware binary image. This configuration parameter is mandatory if *FW_PAYLOAD_ALIGN* is not defined. Compilation errors will result from an incorrect definition of *FW_PAYLOAD_OFFSET* or of *FW_PAYLOAD_ALIGN*, or if neither of these parameters are defined. * **FW_PAYLOAD_ALIGN** - Address alignment constraint where the payload binary will be linked after the end of the base firmware binary in the final *FW_PAYLOAD* firmware binary image. This configuration parameter is mandatory if *FW_PAYLOAD_OFFSET* is not defined. If both *FW_PAYLOAD_OFFSET* and *FW_PAYLOAD_ALIGN* are defined, *FW_PAYLOAD_OFFSET* is used and *FW_PAYLOAD_ALIGN* is ignored. * **FW_PAYLOAD_PATH** - Path to the image file of the next booting stage binary. If this option is not provided then a simple test payload is automatically generated and used as a payload. This test payload executes an infinite `while (1)` loop after printing a message on the platform console. * **FW_PAYLOAD_FDT_ADDR** - Address where the FDT passed by the prior booting stage or specified by the *FW_FDT_PATH* parameter and embedded in the *.rodata* section will be placed before executing the next booting stage, that is, the payload firmware. If this option is not provided, then the firmware will pass the FDT address passed by the previous booting stage to the next booting stage. *FW_PAYLOAD* Example -------------------- The *[qemu/virt]* platforms illustrate how to configure and use a *FW_PAYLOAD* firmware. Detailed information regarding these platforms can be found in the platform documentation files. [qemu/virt]: ../platform/qemu_virt.md