Start porting kernel 2.6.27.8 to qq2440 (3) -- clock initialization
2008-12-12 14:45
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为了保证开发板上各个部件的正常工作,需要设置正确的时钟频率。以2.6.27.8中SMDK2440举例。在arch/arm/mach-s3c2440/march-smdk2440.c中, MACHINE_START/MACHINE_END指定了开发板的配置情况,其中.map_io = smdk2440_map_io 。
在smdk_2440_map_io函数中,调用了s3c24xx_init_clocks(1693440)。1693440就是开发板上时钟晶体的频率。s3c24xx_init_clocks的实现在arch/arm/plat-s3c24xx/cpu.c中:
在smdk_2440_map_io函数中,调用了s3c24xx_init_clocks(1693440)。1693440就是开发板上时钟晶体的频率。s3c24xx_init_clocks的实现在arch/arm/plat-s3c24xx/cpu.c中:
__init s3c24xx_init_clocks(int xtal) 271{ 272 if (xtal == 0) 273 xtal = 12*1000*1000; 274 275 if (cpu == NULL) 276 panic("s3c24xx_init_clocks: no cpu setup?/n"); 277 278 if (cpu->init_clocks == NULL) 279 panic("s3c24xx_init_clocks: cpu has no clock init/n"); 280 else 281 (cpu->init_clocks)(xtal); 282} 可以看到,如果没有指定频率则默认为12MHz, cpu是通过s3c_lookup_cpu得到的,对于2440来说,init_clocks就是s3c244x_init_clocks, 在arch/arm/plat-s3c24xx/s3c244x.c中
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