Introduction to big-endian and small-endian modes of tms320c6713

1. Concept and detailed explanation

There are two main byte storage mechanisms commonly used in computers of various systems: big-endian and little-endian, that is, big-endian mode and little-endian mode.

Let's review two key words first, MSB and LSB:

MSB:Most Significant Bit ------- Most Significant Bit
LSB:Least Significant Bit ------- Least Significant Bit

Big-endian

big-endian: The MSB is stored at the lowest address.

For example, the double-byte number 0x1234 is stored in big-endian format at the starting address 0x00002000:

| data |<-- address
| 0x12 |<-- 0x00002000
| 0x34 |<-- 0x00002001

In Big-Endian, the serial number in the bit sequence is arranged as follows (taking the double-byte number 0x8B8A as an example):

bit | 0 1 2 3 4 5 6 7 | 8 9 10 11 12 13 14 15
------MSB------------------------ ----------LSB
val | 1 0 0 0 1 0 1 1 | 1 0 0 0 1 0 1 0 |
+------------------ --------------------------+
= 0x8 B 8 A

Little-endian

Little-endian: The LSB is stored at the lowest address.

For example, the double-byte number 0x1234 is stored in little-endian format at the starting address 0x00002000:

| data |<-- address
| 0x34 |<-- 0x00002000
| 0x12 |<-- 0x00002001

In Little-Endian, the serial number arrangement in the bit sequence is exactly the opposite of Big-Endian, as follows (taking the double-byte number 0x8B8A as an example):

bit | 15 14 13 12 11 10 9 8 | 7 6 5 4 3 2 1 0
------MSB------------------------ ----------LSB
val | 1 0 0 0 1 0 1 1 | 1 0 0 0 1 0 1 0 |
+----------------- ----------------------------+
= 0x8 B 8 A

2. Storage of arrays in big-endian and small-endian situations:

Take unsigned int value = 0x12345678 as an example, and look at its storage in two byte orders. We can use unsigned char buf[4] to represent value:
Big-Endian: The high bits are stored in the low addresses, as follows:

High address
--------------
buf[3] (0x78) -- Low
buf[2] (0x56)
buf[1] (0x34)
buf[0] (0x12) -- High
---------------
Low address

Little-Endian: The low address stores the low bits, as follows:

High address
--------------
buf[3] (0x12) -- High bit
buf[2] (0x34)
buf[1] (0x56)
buf[0] (0x78) -- Low bit
--------------
low address

3. Big-endian and small-endian conversion method:

Big-Endian is converted to Little-Endian as follows:

#define BigtoLittle16(A) ((((uint16)(A) & 0xff00) >> 8) |
(((uint16)(A) & 0x00ff) << 8))
#define BigtoLittle32(A) ((((uint32 )(A) & 0xff000000) >> 24) |
(((uint32)(A) & 0x00ff0000) >> 8) |
(((uint32)(A) & 0x0000ff00) << 8) |
(((uint32)( A) & 0x000000ff) << 24))

4. Big-endian and small-endian detection methods:

How to check if processor is big-endian or little-endian?

The storage order of the union is that all members are stored starting from the lowest address. This feature can be used to easily obtain whether the CPU uses Little-endian or Big-endian mode to read and write memory .

int checkCPUendian()
{
union
{
unsigned int a;
unsigned char b;
}c;
ca = 1;
return (cb == 1);
}