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Self-modifying code is sometimes used to overcome limitations in a machine's instruction set. For example, in the Intel 8080 instruction set, one cannot input a byte from an input port that is specified in a register. The input port is statically encoded in the instruction itself, as the second byte of a two byte instruction.
For example in a system with an i.MX7D processor and a bootable device which stores the OS (including U-Boot), the on-chip boot ROM sets up the DDR memory controller at first which allows the boot ROM's program to obtain the SoC configuration data from the external bootloader on the bootable device. [5]
Some embedded system designs may also include an intermediary boot sequence step. For example, Das U-Boot may be split into two stages: the platform would load a small SPL (Secondary Program Loader), which is a stripped-down version of U-Boot, and the SPL would do some initial hardware configuration (e.g. DRAM initialization using CPU cache as ...
When a system on a chip (SoC) enters suspend to RAM mode, in many cases, the processor is completely off while the RAM is put in self refresh mode. At resume, the boot ROM is executed again and many boot ROMs are able to detect that the SoC was in suspend to RAM and can resume by jumping directly to the kernel which then takes care of powering on again the peripherals which were off and ...
The Primary Bootloader (PBL), which is stored in the Boot ROM [3] is the first stage of the boot process. This code is written by the chipset manufacturer. [4] The PBL verifies the authenticity of the next stage. On Samsung smartphones, the Samsung Secure Boot Key (SSBK) is used by the boot ROM to verify the next stages. [5]
The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch–execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
In the mid-1990s, a facility for supplying new microcode was initially referred to as the Pentium Pro BIOS Update Feature. [18] [19] It was intended that user-mode applications should make a BIOS interrupt call to supply a new "BIOS Update Data Block", which the BIOS would partially validate and save to nonvolatile BIOS memory; this could be supplied to the installed processors on next boot.
Bootstrapping a compiler has the following advantages: [6] It is a non-trivial test of the language being compiled, and as such is a form of dogfooding.; Compiler developers and bug reporters only need to know the language being compiled.