So when u-Boot is built for a platform that requires SPL, it generate two binaries : SPL (MLO file) and u-Boot image. It shares the same u-Boot’s sources but with a minimal set of code. To handle this limitation, u-Boot adopted the SPL (Secondary Program Loader) approach which consists of creating a very small pre-loader that after configuring and initializing peripherals and the main system memory can load the full blown u-Boot. Second stage – SPLĪ typical u-Boot image is around few hundreds KB size (~300KB) which does not fit inside internal SRAM of most ARM processor. The main goal here is to perform basic peripherals initialization such as PLLs, system clocks setup then find a boot device from which load a bootloader such as u-Boot. In case of a Secure Boot processor it will also verify the code authenticity before its execution.Īt this stage, Boot ROM code is not aware about memory type and different interconnected peripherals. ![]() It contains the very first code which is executed on power-on or reset.ĭepending on the configuration of the bootstrap pins or internal fuses it may decide from which media to load and run the next piece of software. This is the primary program loader residing on a read-only flash memory (ROM) integrated directly into the processor chip.
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