内核时钟初始化函数是s3c24xx_init_clocks(12000000)。
改函数的从start_kernel-->setup_arch(&command_line)-->paging_init(mdesc)-->devicemaps_init(mdesc)-->if (mdesc->map_io)mdesc->map_io();-->mini2440_map_io-->s3c24xx_init_clocks(12000000).所以此函数是各个部分初始化的起点。
s3c24xx_init_clocks(12000000)定义如下:
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void __init s3c24xx_init_clocks(int xtal)
{
if (xtal == 0)
xtal = 12*1000*1000;
if (cpu == NULL)
panic("s3c24xx_init_clocks: no cpu setup?\n");
if (cpu->init_clocks == NULL)
panic("s3c24xx_init_clocks: cpu has no clock init\n");
else
(cpu->init_clocks)(xtal);
}
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这个函数中看到一个cpu,那么这个变量是什么。看文件plat-s3c/init.c:
static struct cpu_table *cpu;它是一个cpu_table类型的指针。如下是其结构定义:
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struct cpu_table {
unsigned long idcode;
unsigned long idmask;
void (*map_io)(void);
void (*init_uarts)(struct s3c2410_uartcfg *cfg, int no);
void (*init_clocks)(int xtal);
int (*init)(void);
const char *name;
};
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这样就不难理解s3c24xx_init_clocks了。那么这个CPU指针具体指向什么呢。在文件cpu.c中有如下定义:
static const char name_s3c2400[] = "S3C2400";
static const char name_s3c2410[] = "S3C2410";
static const char name_s3c2412[] = "S3C2412";
static const char name_s3c2440[] = "S3C2440";
static const char name_s3c2442[] = "S3C2442";
static const char name_s3c2442b[] = "S3C2442B";
static const char name_s3c2443[] = "S3C2443";
static const char name_s3c2410a[] = "S3C2410A";
static const char name_s3c2440a[] = "S3C2440A";
static struct cpu_table cpu_ids[] __initdata = {
{
.idcode = 0x32410000,
.idmask = 0xffffffff,
.map_io = s3c2410_map_io,
.init_clocks = s3c2410_init_clocks,
.init_uarts = s3c2410_init_uarts,
.init = s3c2410_init,
.name = name_s3c2410
},
{
.idcode = 0x32410002,
.idmask = 0xffffffff,
.map_io = s3c2410_map_io,
.init_clocks = s3c2410_init_clocks,
.init_uarts = s3c2410_init_uarts,
.init = s3c2410a_init,
.name = name_s3c2410a
},
{
.idcode = 0x32440000,
.idmask = 0xffffffff,
.map_io = s3c244x_map_io,
.init_clocks = s3c244x_init_clocks,
.init_uarts = s3c244x_init_uarts,
.init = s3c2440_init,
.name = name_s3c2440
},
{
.idcode = 0x32440001,
.idmask = 0xffffffff,
.map_io = s3c244x_map_io,
.init_clocks = s3c244x_init_clocks,
.init_uarts = s3c244x_init_uarts,
.init = s3c2440_init,
.name = name_s3c2440a
},
{
.idcode = 0x32440aaa,
.idmask = 0xffffffff,
.map_io = s3c244x_map_io,
.init_clocks = s3c244x_init_clocks,
.init_uarts = s3c244x_init_uarts,
.init = s3c2442_init,
.name = name_s3c2442
},
{
.idcode = 0x32440aab,
.idmask = 0xffffffff,
.map_io = s3c244x_map_io,
.init_clocks = s3c244x_init_clocks,
.init_uarts = s3c244x_init_uarts,
.init = s3c2442_init,
.name = name_s3c2442b
},
{
.idcode = 0x32412001,
.idmask = 0xffffffff,
.map_io = s3c2412_map_io,
.init_clocks = s3c2412_init_clocks,
.init_uarts = s3c2412_init_uarts,
.init = s3c2412_init,
.name = name_s3c2412,
},
{
.idcode = 0x32412003,
.idmask = 0xffffffff,
.map_io = s3c2412_map_io,
.init_clocks = s3c2412_init_clocks,
.init_uarts = s3c2412_init_uarts,
.init = s3c2412_init,
.name = name_s3c2412,
},
{
.idcode = 0x32443001,
.idmask = 0xffffffff,
.map_io = s3c2443_map_io,
.init_clocks = s3c2443_init_clocks,
.init_uarts = s3c2443_init_uarts,
.init = s3c2443_init,