内核运行之前访问IO

最新推荐文章于 2025-08-16 09:06:58 发布

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最新推荐文章于 2025-08-16 09:06:58 发布

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文章标签：嵌入式

如果要在内核运行之前访问CPU的某些IO端口，直接使用指针方式定义寄存器进行操作即可。例如，在解压内核的时候喂狗，通过操作IO进行，可以这样操作：

在arch/arm/boot/compressed/misc.c文件：

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;

参考include/asm-arm/arch-pxa/uncompress.h文件访问串口的代码：

  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}

可以这样定义：

#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))