First look at ARM cotex-A9

1) The role of resistance

[Pull-up resistor]

       The resistor connected between the power supply and the reference point

       (1) Function: Set the reference point level to high level by default

[Pull-down resistor]

       The resistor between ground and the reference point

       (1) Function: Set the reference point level to low level by default

2) Locality principle

When a program is executed, the data accessed and the instructions executed are often within a local scope.

3) bus

       A group of lines that can connect multiple devices is called a bus.

       (1) CPU bus

           A set of lines connecting the CPU (ALU and controller) to memory and IO devices for transmitting: address, data and control

           Address Lines

           Data cable

           Control Line

       (2) Single bus (ARM)

           Memory and IO devices are connected to the same CPU bus, which is manifested as:

           1. Memory and IO devices are in the same address space (0 - 4G)

           2. The method of accessing memory and IO devices is the same (the instructions are the same)

       (3) Multi-bus (x86)

           Memory and IO devices are connected to different sets of CPU buses, as shown below:

           1. Are the memory and IO devices in the same address space (0 - 4G)?

           2. The method of accessing memory and IO devices is the same (different instructions)

4) RISC & CISC

RISC (Reduced Instruction Set): Functions that can be implemented without hardware can be implemented with software.

CISC (Complex Instruction Set): All functions that can be implemented by hardware are implemented by hardware.

5) Eight working modes of ARM processor

(1) Normal operation

user runs the application

system runs the process context in the kernel

SVC runs the management code of the operating system

(2) Interrupt operation

IRQ (Interrupt Request) runs normal device interrupts

FIQ (Fast Interrupt Request) is used for fast or secure device interrupts

(3) Exception handling

Abort Mode in which the processing program is executed when reading instructions or storing data fails

Undefined Instruction When parsing the instruction, it is found that the instruction is illegal and the mode of running the processing program

(4) Monitor

Coetex-A Safe Mode

6) Permissions

User non-privileged mode

Other privileged modes

7) Register

Concept: A hardware-software interface is also a storage unit. A CPU core register is also a storage unit. The CPU uses the number in the register name to access the register.

Function: R0——R15 general register

R0——R7 non-backup registers

R8——R14 backup register

R13 (SP) Stack pointer register

R14 (LR) saves the return address register

R15 (PC) Program Count (the address of the instruction being read)

CPSR Status Register

SPSR Backup Status Register

8) CPSR        

Status flag (generated during ALU operation)

            (1) N  

Whether the calculated result is a negative number (the highest digit of the saved result)

                  1 Negative

                  0 Positive number

                  Example: 2 - 3 = -1 N = 1

                      0000 0000 0000 0000 0000 0000 0000 0010

                     +1111 1111 1111 1111 1111 1111 1101

                     -----------------------------------------

                      1

                      2 - 1 = 1 N = 0

                      0000 0000 0000 0000 0000 0000 0000 0010

                     +1111 1111 1111 1111 1111 1111 1111

                     -----------------------------------------

                     10

                  int x, y

                  ....

                  if (x > y)

             (2) Z  

Whether the result of the calculation is 0 (the saved result)

                  1 is 0

                  0 is non-zero

                  Example: 2 - 2 = 0 Z = 1

                      0000 0000 0000 0000 0000 0000 0000 0010

                     +1111 1111 1111 1111 1111 1111 1111 1110

                     -----------------------------------------

                     10

                  int x, y

                  ...

                  if (x == y)

             (3) C  

Is there a carry in addition operation?

                  1 Carry

                  0 No carry

                  Is there a borrow in the subtraction operation?

                  1 No borrowing

                  0 There is a borrow

                  Example: 2 - 3 = -1 C = 0

                      0000 0000 0000 0000 0000 0000 0000 0010

                     +1111 1111 1111 1111 1111 1111 1101

                     -----------------------------------------

                      1

                      2 - 3 = -1 C = 0

                      0000 0000 0000 0000 0000 0000 0000 0010

                     -0000 0000 0000 0000 0000 0000 0000 0011

                     -----------------------------------------

                 unsigned int x, y;

                 ...

                 if (x > y)       

              (4) V  

Is the result of the calculation beyond the range of the complement code?

                 1 exceeds the range of the two's complement

                 0 does not exceed the range of the two's complement

                 Example: 0x7fffffff - (-1) = -2^31 V = 1

                     0 0111 1111 1111 1111 1111 1111 1111 1111

                    +0 0000 0000 0000 0000 0000 0000 0000 0000 0001

                    ------------------------------------------

                     0 1 0

                     -2^31 - 1 V = 1

                     -2^31 +(-2^31) V = 1

                     -1 + -1 V = 0

                     1 1111 1111 1111 1111 1111 1111 1111 1111

                     1 1111 1111 1111 1111 1111 1111 1111 1111

                     -----------------------------------------

                     1 1 10

                 Summarize:

                 If the result of the operation is negative (saved), and V = 1, it means that the original (actual) result is positive.

                                 Positive or 0 V = 1, negative

           I bit masks IRQ interrupt

           F bit masks FIQ interrupts

           T bit 1 indicates that the thumb instruction is being executed and the system is in thumb state.

                    0 ARM ARM

           Mode bit 0 - 4bit