ARM系统时钟初始化
Posted 三石居士
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2440时钟体系，12MHz的晶振
6410时钟体系，12MHz的晶振
210时钟体系，24MHz晶振
时钟初始化：1、设置locktime 2、设置分频系数 4、设置CPU到异步工作模式 3、设置fclk
.text .global _start _start: b reset ldr pc, _undefined_instruction ldr pc, _software_interrupt ldr pc, _prefetch_abort ldr pc, _data_abort ldr pc, _not_used ldr pc, _irq ldr pc, _fiq _undefined_instruction: .word undefined_instruction _software_interrupt:.word software_interrupt _prefetch_abort:.word prefetch_abort _data_abort:.word data_abort _not_used:.word not_used _irq:.word irq _fiq:.word reset undefined_instruction: nop software_interrupt: nop prefetch_abort: nop data_abort: nop not_used: nop irq: nop fiq: nop reset: bl set_svc bl disable_watchdog bl disable_interrupt bl disable_mmu bl clock_init bl light_led set_svc: mrs r0, cpsr bic r0, r0, #0x1f orr r0, r0, #0xd3 msr cpsr, r0 mov pc, lr #define pwTCON 0x53000000 disable_watchdog: ldr r0, =pwTCON mov r1, #0x0 str r1, [r0] mov pc, lr disable_interrupt: mvn r1, #0x0 ldr r0, =0x4a000008 str r1,[r0] mov pc, lr disable_mmu: mcr p15,0,r0,c7,c7,0 mrc p15,0,r0,c1,c0,0 bic r0,r0,#0x00000007 mcr p15,0,r0,c1,c0,0 mov pc, lr #define GPBCON 0x56000010 #define GPBDAT 0x56000014 light_led: ldr r0, =GPBCON ldr r1, =0x15400 str r1,[r0] ldr r0, =GPBDAT ldr r1, =0x6bf str r1, [r0] mov pc, lr #define CLKDIVN 0x4c000014 #define MPLLCON 0x4c000008 #define MPLL_405MHZ ((127<<12)|(2<<4)|(1<<0)) clock_init: ldr r0, =CLKDIVN mov r1, #0x5 str r1, [r0] mrc p15,0,r0,c1,c0,0 orr r0,r0,#0xc0000000 mcr p15,0,r0,c1,c0,0 ldr r0, =MPLLCON ldr r1, =MPLL_405MHZ str r1, [r0] mov pc, lr
黄色部分就是时钟初始化，中间一段绿色的是HDIVN不是0的时候，CPU要设置成异步模式，看下面这个
但是在6410里面，设置成异步模式看这个寄存器
第7位设置是否为异步模式，所谓代码里要用bic来清除。第六位是设置是否用PLL之后产生的时钟来提供时钟源
就这图中的这个
代码如下
.text .global _start _start: b reset ldr pc, _undefined_instruction ldr pc, _software_interrupt ldr pc, _prefetch_abort ldr pc, _data_abort ldr pc, _not_used ldr pc, _irq ldr pc, _fiq _undefined_instruction: .word undefined_instruction _software_interrupt:.word software_interrupt _prefetch_abort:.word prefetch_abort _data_abort:.word data_abort _not_used:.word not_used _irq:.word irq _fiq:.word reset undefined_instruction: nop software_interrupt: nop prefetch_abort: nop data_abort: nop not_used: nop irq: nop fiq: nop reset: bl set_svc bl set_peri_port bl disable_watchdog bl disable_interrupt bl disable_mmu bl clock_init bl light_led set_svc: mrs r0, cpsr bic r0, r0, #0x1f orr r0, r0, #0xd3 msr cpsr, r0 mov pc, lr set_peri_port: ldr r0,=0x70000000 orr r0,r0,#0x13 mcr p15,0,r0,c15,c2,4 mov pc,lr #define pwTCON 0x7e004000 disable_watchdog: ldr r0, =pwTCON mov r1, #0x0 str r1, [r0] mov pc, lr disable_interrupt: mvn r1, #0x0 ldr r0, =0x71200014 str r1,[r0] mov pc, lr ldr r0, =0x71300014 str r1, [r0] mov pc, lr disable_mmu: mcr p15,0,r0,c7,c7,0 mrc p15,0,r0,c1,c0,0 bic r0,r0,#0x00000007 mcr p15,0,r0,c1,c0,0 mov pc, lr #define CLK_DIV0 0X7e00f020 #define OTHERS 0x7e00f900 #define MPLLCON 0x7e00f010 #define APLLCON 0x7e00f0c0 #define CLK_SRC 0x7e00f01c #define PLL_VAL ((1<<31)|(266<<16)|(3<<8)|(1<<0)) #define DIV_VAL ((0x0<<0)|(0x1<<9)|(0x1<<8)|(0x3<<12)) clock_init: ldr r0, =CLK_DIV0 ldr r1, =DIV_VAL str r1, [r0] ldr r0, = OTHERS ldr r1, [r0] bic r1, r1, #0xc0 str r1, [r0] ldr r0, =MPLLCON ldr r1, =PLL_VAL str r1,[r0] ldr r0, =CLK_SRC mov r1, #0x3 str r1, [r0] mov pc, lr #define GPBCON 0x7f008820 #define GPBDAT 0x7f008804 light_led: ldr r0, =GPBCON ldr r1, =0x1111 str r1,[r0] ldr r0, =GPBDAT ldr r1, =0xe str r1, [r0] mov pc, lr
黄色部分就是设置时钟的，能看懂手册，就能写代码。
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