Access Io before the kernel runs

If you want to access some of the CPU's I/O ports before the kernel runs, use the pointer to define the register for operations. For example, you can run the IO command to feed the dog when extracting the kernel:

In the ARCH/ARM/boot/compressed/Misc. c file: 307 arch_decomp_setup (); 308 309 makecrc (); 310 * (volatile unsigned long *) 0x40e00054) & = (~ (3 <28); // abing gpaf0_l 311 * (volatile unsigned long *) 0x40e0001c) = (1 <14 ); // abing gpdr0 312 * (volatile unsigned long *) 0x40e00024) = (1 <14); // abing gpcr0 313 putstr ("Uncompressing Linux... "); 314 * (volatile unsigned long *) 0x40e00018) = (1 <14); // abing gpsr0 315 gunzip (); 316 * (volatile unsigned long *) 0x40e00024) = (1 <14); // abing gpcr0 317 putstr ("done, booting the kernel. \ n "); 318 return output_ptr; refer to include/ASM-arm/arch-PXA/uncompress. code for accessing the serial port of an H file:

  12#define FFUART          ((volatile unsigned long *)0x40100000)  13#define BTUART          ((volatile unsigned long *)0x40200000)  14#define STUART          ((volatile unsigned long *)0x40700000)  15  16#define UART            FFUART  17  18  19static __inline__ void putc(char c)  20{  21        while (!(UART[5] & 0x20));  22        UART[0] = c;  23}  24  25/*  26 * This does not append a newline  27 */  28static void putstr(const char *s)  29{  30        while (*s) {  31                putc(*s);  32                if (*s == '\n')  33                        putc('\r');  34                s++;  35        }  36}

It can be defined as follows:

#define __raw_readl(a)    (*(volatile unsigned int *)(a))#define __raw_writel(v,a) (*(volatile unsigned int *)(a) = (v))#define __raw_readw(a)    (*(volatile unsigned short *)(a))#define __raw_writew(v,a) (*(volatile unsigned short *)(a) = (v))