在調試MSP430G系列的單片機的過程，發現不怎么的，時鐘頻率發生了變化，時間一下都對不上了。查收些資料說，DCO的值有可能被擦除了導致時鐘不對的。細想一下，好像是在調試的過程中，出現調試不了的現象就在IAR里點擊的“Erase memory”。把查找的資料記錄下來，所以就有這篇文章。

問題描述

因為DCO校準值在MCU出廠時保存于信息段A，一般是不允許清除信息段A的。

且示例代碼中，有如下語句：

if (CALBC1_1MHZ ==0xFF || CALDCO_1MHZ == 0xFF) { while(1);// If calibration constants erased // do not load, trap CPU!! } BCSCTL1 = CALBC1_1MHZ; // Set range DCOCTL = CALDCO_1MHZ; // Set DCO step + modulation

可以看出在啟動時都先檢查DCO1MHZ的校準值是否為0xFF，是則進入while(1)死循環。
正常情況下因為信息段A不清除沒問題的，但是我測試BSL下載時，故意給錯誤的BSL密碼，導致FLASH都被擦除，發現轉載DCO校準值的信息段A也被清掉了，于是程序運行到上面的代碼時即進入死循環。

解決辦法

針對于這種DCO數據被擦除的情況，一般的解決辦法是，通過利用Timer捕捉外部的32.768K晶振或是時鐘源，然后得到1M，8M或是12Mhz之類的DCO的數值，然后在直接寫入segment flashA里面。
有兩個解決方案供選擇：

1、外接晶體，用晶體配合timer校正DCO，TI的msp4300ware有源代碼。如下：

/******************************************************************************* * * MSP430 CODE EXAMPLE DISCLAIMER * * MSP430 code examples are self-contained low-level programs that typically * demonstrate a single peripheral function or device feature in a highly * concise manner. For this the code may rely on the device's power-on default * register values and settings such as the clock configuration and care must * be taken when combining code from several examples to avoid potential side * effects. Also see for a GUI- and * for an API functional library-approach to peripheral configuration. * * --/COPYRIGHT-- //******************************************************************************/ // MSP430G2xx1 Demo - DCO Calibration Constants Programmer // // NOTE: THIS CODE REPLACES THE TI FACTORY-PROGRAMMED DCO CALIBRATION // CONSTANTS LOCATED IN INFOA WITH NEW VALUES. USE ONLY IF THE ORIGINAL // CONSTANTS ACCIDENTALLY GOT CORRUPTED OR ERASED. // // Description: This code re-programs the G2xx1 DCO calibration constants. // A software FLL mechanism is used to set the DCO based on an external // 32kHz reference clock. After each calibration, the values from the // clock system are read out and stored in a temporary variable. The final // frequency the DCO is set to is 1MHz, and this frequency is also used // during Flash programming of the constants. The program end is indicated // by the blinking LED. // ACLK = LFXT1/8 = 32768/8, MCLK = SMCLK = target DCO // //* External watch crystal installed on XIN XOUT is required for ACLK *// // // MSP430G2xx1 // --------------- // /|\| XIN|- // | | | 32kHz // --|RST XOUT|- // | | // | P1.0|--> LED // | P1.4|--> SMLCK = target DCO // // A. Dannenberg // Texas Instruments Inc. // May 2010 // Built with CCS Version 4.2.0 and IAR Embedded Workbench Version: 3.42A //****************************************************************************** #include #define DELTA_1MHZ 244 // 244 x 4096Hz = 999.4Hz #define DELTA_8MHZ 1953 // 1953 x 4096Hz = 7.99MHz #define DELTA_12MHZ 2930 // 2930 x 4096Hz = 12.00MHz #define DELTA_16MHZ 3906 // 3906 x 4096Hz = 15.99MHz unsigned char CAL_DATA[8]; // Temp. storage for constants volatile unsigned int i; int j; char *Flash_ptrA; // Segment A pointer void Set_DCO(unsigned int Delta); int main(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT for (i = 0; i < 0xfffe; i++); // Delay for XTAL stabilization P1OUT = 0x00; // Clear P1 output latches P1SEL = 0x10; // P1.4 SMCLK output P1DIR = 0x11; // P1.0,4 output j = 0; // Reset pointer Set_DCO(DELTA_16MHZ); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Set_DCO(DELTA_12MHZ); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Set_DCO(DELTA_8MHZ); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Set_DCO(DELTA_1MHZ); // Set DCO and obtain constants CAL_DATA[j++] = DCOCTL; CAL_DATA[j++] = BCSCTL1; Flash_ptrA = (char *)0x10C0; // Point to beginning of seg A FCTL2 = FWKEY + FSSEL0 + FN1; // MCLK/3 for Flash Timing Generator FCTL1 = FWKEY + ERASE; // Set Erase bit FCTL3 = FWKEY + LOCKA; // Clear LOCK & LOCKA bits *Flash_ptrA = 0x00; // Dummy write to erase Flash seg A FCTL1 = FWKEY + WRT; // Set WRT bit for write operation Flash_ptrA = (char *)0x10F8; // Point to beginning of cal consts for (j = 0; j < 8; j++) *Flash_ptrA++ = CAL_DATA[j]; // re-flash DCO calibration data FCTL1 = FWKEY; // Clear WRT bit FCTL3 = FWKEY + LOCKA + LOCK; // Set LOCK & LOCKA bit while (1) { P1OUT ^= 0x01; // Toggle LED for (i = 0; i < 0x4000; i++); // SW Delay } } void Set_DCO(unsigned int Delta) // Set DCO to selected frequency { unsigned int Compare, Oldcapture = 0; BCSCTL1 |= DIVA_3; // ACLK = LFXT1CLK/8 TACCTL0 = CM_1 + CCIS_1 + CAP; // CAP, ACLK TACTL = TASSEL_2 + MC_2 + TACLR; // SMCLK, cont-mode, clear while (1) { while (!(CCIFG & TACCTL0)); // Wait until capture occured TACCTL0 &= ~CCIFG; // Capture occured, clear flag Compare = TACCR0; // Get current captured SMCLK Compare = Compare - Oldcapture; // SMCLK difference Oldcapture = TACCR0; // Save current captured SMCLK if (Delta == Compare) break; // If equal, leave "while(1)" else if (Delta < Compare) { DCOCTL--; // DCO is too fast, slow it down if (DCOCTL == 0xFF) // Did DCO roll under? if (BCSCTL1 & 0x0f) BCSCTL1--; // Select lower RSEL } else { DCOCTL++; // DCO is too slow, speed it up if (DCOCTL == 0x00) // Did DCO roll over? if ((BCSCTL1 & 0x0f) != 0x0f) BCSCTL1++; // Sel higher RSEL } } TACCTL0 = 0; // Stop TACCR0 TACTL = 0; // Stop Timer_A BCSCTL1 &= ~DIVA_3; // ACLK = LFXT1CLK }