Link and program relationship

DDR = double data rate double rate synchronous dynamic random memory. Strictly speaking, DDR should be called ddr sdram, which is often called DDR,

Now let's analyze the DDR initialization.

A program can be divided into code segments, data segments, and BSS segments.

Code segment: commands and other things

Data Segment: Global or static variable with an initial value and the initial value is not 0

BSS segment: global variables and static variables with an initial value of 0 or no initial value, for example:

Volatile int I = 0;

 

Volatile Int J = 0x12345678;

Volatile int K = 0;

Volatile int g;

/* Set gpm0, 1, 2, 3 to the output pin */

* Gpmcon = 0x1111;

I, K, and G exist in BSS segments.

J exists in the Data Segment

For * gpmcon = 0x1111; this is suitable for the code segment.

First, let's take a look at program burning:

1. Our program was first written on NAND Flash.

2. When we set it to NAND boot, 6410 pieces of memory will have 8 KB, And the CPU will copy the content of the first 8 KB of NAND Flash to ram through internal hardware (the starting address is 00000000).

Now there is a problem: What should we do if the number of programs we write exceeds 8 KB?

If our program exceeds 8 K, we need to use DDR and copy the entire program to DDR. Where can we copy the program to DDR, my DDR has m space. At this time, the link address is used, that is, the program will be copied to the link address.

Here is an example of a link script.

Sections // represents a segment

{

. = 0x5000;/**. indicates the current address. Assign the address 0 x, that is, the link address of the entire program **/

. Text: {/**. You can modify the text segment name ********/

Start. O/** start. O indicates the entire start. o file (including code, data, and BSS segments )**/

* (. Text)/** code segment for storing all other files **/

}

. Data: {/** data Segment **/

* (. Data)/** data segment of all other files **/

}

Bss_start =.;/* defines the variable and assigns the variable bss_start to the current address (the current address is the address discharged in sequence )*/

. Bss :{

* (. Bss)/** Bss segments of all other files **/

}

Bss_end =.;/** defines the variable and assigns the variable bss_end to the current address. Similarly, the current address is the address 6 after the last bss address discharged in sequence **/

}

The comments are already very detailed.

Relocation: we have already mentioned the concept of relocation.

When the link address we set is not 0x50000000 (for example, 0 x), we need to relocate it. That is, after the hardware copies the original program to the internal 8 k ram, because the link address is not 0x00, the relocation function will copy the program to the starting address 0x50000000.

Obviously, a piece of code must be run before the relocation is completed. Why can this code be run? This involves another concept-location-independent code, because location-independent code is used (the so-called location-independent code can be run at any connection location ).

Location-independent code usage:

1. Use the relative commands B and bl when redirecting

2. Do not access global variables or static variables

Summary:

1. When running the program, it should be located at its link address. Assume that its link address is 0x50000000.

2. The hardware determines that the program starts to run from 0 at the beginning, so it needs to be relocated (the previous code segment copies the program to the link address)

3. Why can the previous code run? Because location-independent codes (B and bl commands) are used)

Finally, let's analyze the startup process of the entire program:

1. If we burn the generated axf image file to nand flash, set the link address to 0x00000100.

2. An on-chip hardware automatically copies 8 K to OK6410 in-chip memory

3. Then start running from address zero

4. Move the program to the link address.

5. Finally, use the location-related code BL to jump to the connection and execute it.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Then execute the program 0x100 here.   The location code is redirected here. Zero x 00000000

Copy the program Zero x 00000100

8 K

Ok6410-bit RAM

8 K 59.9 K Zero X 00000000

Nand flash

Assume 59.9 K AXF file burning