Embedded Systems Programming

1. Embedded Systems Programming ARM programmer’s model and assembler

2. Memory Formats • The ARM views memory as a linear collection of bytes numbered upwards from zero. Bytes 0 to 3 hold the first stored word, bytes 4 to 7 the second and so on. The ARM can treat words in memory as being stored either in Big Endian or Little Endian format. • A word is 32 bits • Addresses are 32 bits

3. Little endian addresses of bytes within words • In little endian format, the lowest numbered byte in a word is considered the word’s least significant byte, and the highest numbered byte the most significant. Byte 0 of the memory system is therefore connected to data lines 7 through 0.

4. Big endian addresses of bytes within words • In big endian format, the most significant byte of a word is stored at the lowest numbered byte and the least significant byte at the highest numbered byte. Byte 0 of the memory system is therefore connected to data lines 31 through 24.

5. ARM processor modes

6. The ARM register set

8. Program Status Register format • In user programs only the top 4 bits of the CPSR are relevant • N - the result was negative • Z - the result was zero • C - the result produced a carry out • V - the result generated an arithmetic overflow • I, F – interrupt enable bits • T – instruction set (Thumb/ARM)

9. The CPSR mode bits

10. Exception processing modes

11. ARM 7 internals

12. The ARM instruction set • a) Data processing instructions • b) Data transfer instructions • c) Control flow & conditional execution • d) Special instructions

13. Data processing instructions • ALL operands are 32-bits wide and either: • come from registers, or are literals (´immediate´ values ) specified in the instruction • The result, if any, is 32-bits wide and goes into a register • except long multiplies generate 64-bit results • All operand and result registers are specified independently