第四講DSP外設(shè)應(yīng)用之系統(tǒng)時鐘

1、第四講 DSP外設(shè)應(yīng)用之系統(tǒng)時鐘 系統(tǒng)時鐘，即為各個模塊產(chǎn)生所需要的時鐘，如C55x core、慢速外設(shè)（Slow Peripherals），快速外設(shè)（Fast Peripherals）以及其它外設(shè)所需的基準時鐘。系統(tǒng)時鐘的設(shè)置是任何一個可編程器件必須進行的初始化操作。 在DSP5502中，系統(tǒng)的時鐘初始化語句為：PLL_setFreq(1, 0xC, 0, 1, 3, 3, 0);該語句為CSL（Chip Support Library）庫函數(shù)語句，在進行時鐘設(shè)置時，系統(tǒng)調(diào)用該API初始化函數(shù)，以完成系統(tǒng)設(shè)置，對于C55x 5502所涉及的時鐘寄存器如下表所示：系統(tǒng)涉及的函數(shù)原型為void

2、PLL_setFreq (Uint16 mode, Uint16 mul, Uint16 div0, Uint16 div1, Uint16 div2,Uint16 div3, Uint16 oscdiv);Uint16 mode / PLL mode /PLL_PLLCSR_PLLEN_BYP ASS_MODE /PLL_PLLCSR_PLLEN_PLL_MODEUint16 mul / Multiply factor, Valid values are (multiply by) 2 to 15.Uint16 div0 / Sysclk 0 Divide Down, Valid value

3、s are 0, (divide by 1) /to 31 (divide by 32)Uint16 div1 / Sysclk1 Divider, Valid values are 0, 1, and 3 corresponding/to divide by 1, 2, and 4 respectivelyUint16 div2 / Sysclk2 Divider, Valid values are 0, 1, and 3 /corresponding to divide by 1, 2, and 4 respectivelyUint16 div3 / Sysclk3 Divider, Va

4、lid values are 0, 1 and 3 /corresponding to divide by 1, 2 and 4 respectivelyUint16 oscdiv / CLKOUT3(DSP core clock) divider,Valid values are 0 /(divide by 1) to 31 (divide by 32)程序中，對于MODE,則5502有兩種模式：PLL旁路模式和PLL使能模式，前者是時鐘未經(jīng)PLL進行倍頻，而后者使用PLL功能。由于目前無源晶振生產(chǎn)工藝限制，其所能產(chǎn)生的頻率超過30即會有較大的誤差，而5502最高可達到300M時鐘，一般需要

5、使能PLL功能。其它參數(shù)均為各除法器的值，查詢相應(yīng)的寄存器即可完成。表1 所涉及的PLL寄存器及其各相關(guān)位PLLCSR PLLEN, PLLPWRDN, OSCPWRDN, PLLRST, LOCK, STABLEPLLM PLLMPLLDIV0 PLLDIV0, D0ENPLLDIV1 PLLDIV1, D1ENPLLDIV2 PLLDIV2, D2ENPLLDIV3 PLLDIV3, D3ENOSCDIV1 OSCDIV1, OD1ENWAKEUP WKEN0, WKEN1, WKEN2, WKEN3CLKMD CLKMD0CLKOUTSRCLKOUTDIS, CLKOSEL圖1 系統(tǒng)時鐘

6、發(fā)生器圖2 晶振及其時鐘產(chǎn)生電路圖3 內(nèi)部時鐘頻率范圍值圖4 時鐘發(fā)生器寄存器附各個寄存器相關(guān)位說明(1) PLL Control / Status Register (PLLCSR) (0x1c80)nSTABLE6R1Oscillator output stable. This bit indicates if the OSCOUT output has stabilized. STABLE = 0: Oscillator output is not yet stable. Oscillator counter is not done counting 41,032 reference c

7、lock cycles.STABLE = 1: Oscillator output is stable. This is true if any one of the three cases is true:a) Oscillator counter has finished counting.b) Oscillator counter is disabled.c) Test mode.LOCK5R0Lock mode indicator. This bit indicates whether the clock generator is in its lock mode.LOCK = 0:

8、The PLL is in the process of getting a phase lock.LOCK = 1: The clock generator is in the lock mode. The PLL has a phase lock and the output clock of the PLL has the frequency determined by the PLLM register and PLLDIV0 register.PLLRST3R/W1Asserts RESET to PLLPLLRST = 0: PLL reset releasedPLLRST = 1

9、: PLL reset assertedOSCPWRDN2R/W0Sets internal oscillator to power-down modeOSCPWRDN = 0: Oscillator operationalOSCPWRDN = 1: Oscillator set to power-down mode based onstate of CLKMD0 bit of Clock Mode Control Register (CLKMD).When CLKMD0 = 0, the internal oscillator is set to power-down mode when t

10、he clock generator is set to its idle mode CLKIS bit of the IDLE Status Register (ISTR) becomes 1.When CLKMD0 = 1, the internal oscillator is set to power-down mode immediately after the OSCPWRDN bit is set to 1.PLLPWRDN1R/W0Selects PLL power downPLLPWRDN = 0: PLL operational PLLPWRDN = 1: PLL place

11、d in power-down statePLLEN0R/W0PLL mode enable. This bit controls the multiplexer before dividers D1, D2, and D3.PLLEN = 0: Bypass mode. Divider D1 and PLL are bypassed. SYSCLK1 to 3 divided downdirectly from input reference clock. PLLEN = 1: PLL mode. Divider D1 and PLL are not bypassed. SYSCLK1 to

12、 3 divided down from PLL output.(2) PLL Multiplier Control Register (PLLM)15-54-0ReservedPLLMPLLM4:0R/W00000PLL multiplier-selectPLLM = 0000000001: ReservedPLLM = 00010: Times 2PLLM = 00011: Times 3PLLM = 00100: Times 4PLLM = 00101: Times 5PLLM = 00110: Times 6PLLM = 00111: Times 7PLLM = 01000: Time

13、s 8PLLM = 01001: Times 9PLLM = 01010: Times 10PLLM = 01011: Times 11PLLM = 01100: Times 12PLLM = 01101: Times 13PLLM = 01110: Times 14PLLM = 01111: Times 15PLLM = 1000011111: Reserved(3) PLL Divider 0 Register (PLLDIV0) (Prescaler)1514-54-0D0ENReservedPLLDIV0D0EN15R/W1Divider D0 enableD0EN = 0: Divi

14、der 0 disabledD0EN = 1: Divider 0 enabledPLLDIV04:0R/W00000Divider D0 ratioPLLDIV0 = 00000: Divide by 1PLLDIV0 = 00001: Divide by 2PLLDIV0 = 00010: Divide by 3.PLLDIV0 = 11111: Divide by 32(4)PLL Divider1 Register (PLLDIV1) for SYSCLK11514-54-0D1ENReservedPLLDIV1D1EN15R/W1Divider D1 enableD1EN = 0:

15、Divider 1 disabledD1EN = 1: Divider 1 enabledPLLDIV14:0R/W00011Divider D1 ratio (SYSCLK1 divider)PLLDIV1 = 00000: Divide by 1PLLDIV1 = 00001: Divide by 2PLLDIV1 = 00010: ReservedPLLDIV1 = 00011: Divide by 4PLLDIV1 = 0010011111: ReservedPLLDIV2和PLLDIV3的位定義與PLLDIV1完全一樣，在此不再重復(fù)寫了。(5) Oscillator Divider1

16、 Register (OSCDIV1) for CLKOUT31514-54-0OD1ENReservedOSCDIV1OD1EN15R/W0Divider D0 enableD0EN = 0: Divider 0 disabledD0EN = 1: Divider 0 enabledOSCDIV14:0R/W00000Divider D0 ratioPLLDIV0 = 00000: Divide by 1PLLDIV0 = 00001: Divide by 2PLLDIV0 = 00010: Divide by 3.PLLDIV0 = 11111: Divide by 32(6) CLKOUT3 Select Register (CK3SEL)15-43-0ReservedCK3SELCK3SEL3:0R/W1011Output on C