init_pll.asm

DSP中用MCBSP模拟I2C接口的程序.其中DSP的型号是C5416

* filename : init_pll.asm *
* -initialize the CPU clock (10MHz crystal is used) *

     .mmregs
     .def       _INIT_PLL
     .text

_INIT_PLL:

;        stm     #0006h,BSCR             ;clock out div by 1 and enable bus hold
;-- 1. set clock mode to DIV mode. In order to change PLLNDIV, PLLCOUNT etc
        stm     #0,CLKMD
wait_div_mode:
        bitf    *(CLKMD),#1           	;test if PLLSTSATUS=0
        bc      wait_div_mode,TC		;if not move on(PLL mode)

;-- 2. set clock mode to PLL mode
        stm     #0111011111111111b,CLKMD
                ;0111~~~~~~~~~~~~       ;PLL multiplier, freq = PLLMUL + 1 
                ;~~~~0~~~~~~~~~~~       ;PLLDIV, pll divide mode
                ;~~~~~11111111~~~       ;PLLCOUNT, pll lock time, I/P clk X 16
                ;~~~~~~~~~~~~~1~~       ;PLLONOFF
                ;~~~~~~~~~~~~~~1~       ;PLLNDIV, pll divide mode
                ;~~~~~~~~~~~~~~~1       ;PLLSTATUS, pll mode(read only)
;-- 3. wait for PLL lock
wait_pll_mode:
        bitf    *(CLKMD),#1
        bc      wait_pll_mode,NTC
        NOP
     	
     	LDM  PMST,A                        ;
     	OR  #4H,A          ;enable CLKOUT signal
     	STLM A,PMST                        ;
     	nop
     	nop
     	RET