英语翻译
Many applications written for ARM-based systems are embedded applications that are
contained in ROM and execute on reset.There are a number of factors that must be
considered when writing embedded operating systems,or embedded applications that
execute from reset without an operating system,including:
• Remapping ROM to RAM,to improve execution speed.
• Initializing the execution environment,such as exception vectors,stacks,I/Os.
• Initializing the application.
– For example,copying initialization values for initialized variables from ROM
to RAM and resetting all other variables to zero.
• Linking an embedded executable image to place code and data in specific locations
in memory.
For an embedded application without an operating system,the code in ROM must provide
a way for the application to initialize itself and start executing.No automatic
initialization takes place on reset,therefore the application entry point must perform
some initialization before it can call any C code.
The initialization code,located at address zero after reset,must:
• Mark the entry point for the initialization code.
• Set up exception vectors.
• Initialize the memory system.
• Initialize the stack pointer registers.
• Initialize any critical I/O devices.
• Initialize any RAM variables required by the interrupt system.
• Enable interrupts (if handled by the initialization code).
• Change processor mode if necessary.
• Change processor state if necessary.
After the environment has been initialized,the sequence continues with the application
initialization and should enter the C code.
大体意思就行·