ARM 嵌入式学习笔记 (一)

I. Programmer's Model
1. ARM instruction set
Branch instructions
Data-processing instructions
Status register transfer instructions
Load and store instructions
Coprocessor instructions
Exception-generating instructions

2. Processor modes
Processor mode Description
---------------- -------------------------------------------------------
User usr Normal program execution mode
FIQ fiq Supports a high-speed data transfer or channel process
IRQ irq Used for general-purpose interrupt handling
Supervisor svc A protected mode for operating system
Abort abt Implements virtual memory and/or memory protection
Undefined und Support software emulation of hardware coprocessors
System sys Runs privileged operating system tasks

3. Registers
(1) 31 general-purpose registers, including PC.
(2) 6 status registers, these registers are also 32 bits, but only 12 of
32 bits are allocated or need to be implemented.
(3) At any time, 15 general-purpose registers (R0~R14), one or two status
registers and the program counter are visible.
(4) The general-purpose registers R0~R15 can be split into three groups:
The unbanked registers: R0~R7
The banked registers: R8~R15
Register 15, the PC, is described in the Program counter
(5) Banked registers means that each of them refers to the same 32-bit
physical register in all processor modes; Unbanked registers means
the physical register referred to by each of them depends on the
current processor mode.

4. Exceptions
(1)ARM supports seven types of exception, following table lists the types
of exception and the processor mode that is used to process that
exception:
-----------------------------------------------------------------------
Exception Mode Normal High Vector
adddress address
-----------------------------------------------------------------------
Reset Supervisor 0x00000000 0xFFFF0000
Undefined Undefined 0x00000004 0xFFFF0004
Software Interupt Supervistor 0x00000008 0xFFFF0008
Prefetch Abort Abort 0x0000000C 0xFFFF000C
Data Abort Abort 0x00000010 0xFFFF0010
IRQ (interupt) IRQ 0x00000018 0xFFFF0018
FIQ (fase interupt) FIQ 0x0000001C 0xFFFF001C
-----------------------------------------------------------------------

Note: The normal vector at address 0x000014 and the high vector address
at 0xFFFF0014 are not normally used and are reserved for furture
expansion.
(2) An interupt handler that wishes to store its return link on the stack
might use instrcutions of following form at its entry point:

SUB R14, R14, #4
STMFD SP!, {<other_registers>, R14}

and return using the instruction:

LDMFD SP!, {<other_registers>, PC}^

(3) Exception priorities
---------------------------------------------
Priority Exception
---------------------------------------------
1 Reset
---------------------------------------------
2 Data Abort
---------------------------------------------
3 FIQ
---------------------------------------------
4 IRQ
---------------------------------------------
5 Prefetch Abort
---------------------------------------------
6 Undefined instruction
SWI
---------------------------------------------

5. Memory and memory-mapped I/O
(1) Address align
ARM address is word-aligned which means that the address is divisible
by 4(actually the last two bits of that address are 0)

(2) Endianness
In a little-endian memory system:
A byte or halfword at word-aligned address is the least significant
byte or halfword within the word at that address

In a big-endian memory system:
A byte or halfword at word-aligned address is the most significant
byte or halfword with the word at that address

(3) Memory-mapped I/O
This uses special memory addresses which supply I/O functions when
they loaded from or stored to.