Shulou(Shulou.com)06/02 Report--

The last article was about the process of compiling and executing the source files of the program through gcc under linux. And the preparation of makefile files, and finally output myhello word in the terminal platform!

With this foundation, what we will learn this time is to complete the hardware implementation on ARM through the code generated by linux compilation. Because it does not involve system migration, so it is still bare-board program development.

1. Source code writing

ARM bare board program requires code raw materials mainly include: Assembly files, C files, makefile files. Each file has its own function.

(1) compilation document

Finish closing the watchdog; configure the clock; initialize the sdram; settings stack; and jump to the C function execution entry (equivalent to the main function), as follows (this routine does not need to configure the clock and sdram).

@ * * @ File:crt0.S@ function: transfer to C program @ * * Note: the normal assembler also needs to initialize the clock SDRAM function, but not required for lighting LED. Directly use 12Mhz.text.global _ start_start: @ at the beginning of the code snippet of the program, each section in the link script defines ldr r0maide0x53000000 @ watchdog control register address (32-bit address assignment statement, R0 address is 0x53000000) @ ldr and mov is the difference Ldr transmits 32-bit data While mov can only pass 8 digits mov R1, # 0x0 @ immediately assign values to R1 register str R1, [R0] @ give data in R1 register 0x0 to R0 address @ the above three statements assign watchdog control registers 0 ldr sp = 4percent 1024 @ sets the heap to jump to the main function with a size of 4K (before NAND FLASH 4k) bl main @ At the same time, the next instruction address haltloop is saved:

(2) C file

The amount of code compiled is relatively small, only some necessary initialization functions are performed, and the real function part is in the C file. C file mainly executes: register address macro definition, peripheral initialization, function realization and so on.

The led pin lit by this example is GPF4, so you need to consult the reference manual of 2440 to see the relevant register address of GPF. The main configured registers are GPFCON (control register) and GPFDAT (data register). GPFCON mainly controls the working mode of the pin (modes are: input, output, reuse), in which every two bits control the state of one pin, as can be seen from the following figure:

The high and low level of the pin is controlled by GPFDAT, and each bit controls one pin, as shown in the figure:

Therefore, it is very important to learn to read the chip manual, understand each register and program, and at the same time master the shift operation, which is more commonly used in register programming. The code of this part is as follows:

# define GPFCON (* volatile unsigned long*) 0x56000050) # define GPFDAT (* (volatile unsigned long*) 0x56000054) # define GPFUP (* (volatile unsigned long*) 0x56000058) # define GPIO_Pin_0 ((volatile unsigned char) 0x00) # define GPIO_Pin_1 ((volatile unsigned char) 0x01) # define GPIO_Pin_2 ((volatile unsigned char) 0x02) # define GPIO_Pin_3 ((volatile) Unsigned char) 0x03) # define GPIO_Pin_4 ((volatile unsigned char) 0x04) int main () {GPFCON = 0X01

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