源代碼 #define MAX44009_ADDR 0x96 // begin definition of slave addresses for MAX44009 #define INT_STATUS 0x00 #define INT_ENABLE 0x01 #define CONFIG_REG 0x02 #define HIGH_BYTE 0x03 #define LOW_BYTE 0x04 #define THRESH_HIGH 0x05 #define THRESH_LOW 0x06 #define THRESH_TIMER 0x07 // end definition of slave addresses for MAX44009 extern float SCALE_FACTOR; // captures scaling factors to map from % brightness to PWM float currentBright_pct; // the current screen brightness, in % of maximum float desiredBright_pct; // the desired screen brightness, in % of maximum float stepSize; // the step size to use to go from the current // brightness to the desired brightness uint8 lightReadingCounter; /** * Function: SetPWMDutyCycle * * Arguments: uint16 dc - desired duty cycle * * Returns: none * * Description: Sets the duty cycle of a 16-bit PWM, assuming that in this * architecture, 0x0000 = 0% duty cycle * 0x7FFF = 50% and 0xFFFF = 100% **/ extern void SetPWMDutyCycle(uint16 dc); /** * Function: I2C_WriteByte * * Arguments: uint8 slaveAddr - address of the slave device * uint8 command - destination register in slave device * uint8 data - data to write to the register * * Returns: ACK bit * * Description: Performs necessary functions to send one byte of data to a * specified register in a specific device on the I2C bus **/ uint8 2C_WriteByte(uint8 slaveAddr, uint8 command, uint8 data); /** * Function: I2C_ReadByte * * Arguments: uint8 slaveAddr - address of the slave device * uint8 command - destination register in slave device * uint8 *data - pointer data to read from the register * * Returns: ACK bit * * Description: Performs necessary functions to get one byte of data from a * specified register in a specific device on the I2C bus **/ uint8 I2C_ReadByte(uint8 slaveAddr, uint8 command, uint8* data); /** * Function: getPctBrightFromLuxReading * * Arguments: float lux - the pre-computed ambient light level * * Returns: The % of maximum brightness to which the backlight should be set * given the ambient light (0 to 1.0) * * Description: Uses a function to map the ambient light level to a backlight * brightness by using a predetermined function **/ float getPctBrightFromLuxReading(float lux); /** * Function: mapPctBrighttoPWM * * Arguments: float pct * * Returns: PWM counts needed to achieve the specified % brightness (as * determined by some scaling factors) **/ uint16 mapPctBrighttoPWM(float pct); /** * Function: getLightLevel * * Arguments: n/a * * Returns: the ambient light level, in lux * * Description: Reads both the light registers on the device and returns the * computed light level **/ float getLightLevel(void); /** * Function: stepBrightness * * Arguments: n/a * * Returns: n/a * * Description: This function would be called by an interrupt. It looks at the * current brightness setting, then the desired brightness setting. * If there is a difference between the two, the current brightness * setting is stepped closer to its goal. **/ void stepBrightness(void); /** * Function: timerISR * * Arguments: n/a * * Returns: n/a * * Description: An interrupt service routine which fires every 100ms or so. This * handles all the ambient light sensor and backlight * control code. **/ void timerISR(void); void main() { SetupMicro(); // some subroutine which initializes this CPU I2C_WriteByte(MAX44009_ADDR, CONFIG_REG, 0x80); // set to run continuously lightReadingCounter = 0; stepSize = .01; currentBright_pct = 0.5; desiredBright_pct = 0.5; SetPWMDutyCycle(mapPctBrighttoPWM(currentBright_pct)); InitializeTimerInterrupt(); // set this to fire every 100ms while(1) { // do whatever else you need here, the LCD control is done in interrupts Idle(); } } // main routine // the point at which the function clips to 100% #define MAXIMUM_LUX_BREAKPOINT 1254.0 float getPctBrightFromLuxReading(float lux) { if (lux > MAXIMUM_LUX_BREAKPOINT) return 1.0; else return (9.9323*log(x) + 27.059)/100.0; } // getPctBrightFromLuxReading uint16 mapPctBrighttoPWM(float pct) { return (uint16)(0xFFFF * pct * SCALE_FACTOR); } // mapPctBrighttoPWM float getLightLevel(void) { uint8* lowByte; uint8* highByte; uint8 exponent; uint8 mantissa; float result; I2C_ReadByte(MAX44009_ADDR, HIGH_BYTE, highByte); I2C_ReadByte(MAX44009_ADDR, LOW_BYTE, lowByte); exponent = (highByte & 0xF0) >> 4;// upper four bits of high byte register mantissa = (highByte & 0x0F) << 4;// lower four bits of high byte register = // upper four bits of mantissa mantissa += lowByte & 0x0F; // lower four bits of low byte register = // lower four bits of mantissa result = mantissa * (1 << exponent) * 0.045; return result; } //getLightLevel void stepBrightness(void) { // if current is at desired, don't do anything if (currentBright_pct == desiredBright_pct) return; // is the current brightness above the desired brightness? else if (currentBright_pct > desiredBright_pct) { // is the difference between the two less than one step? if ( (currentBright_pct-stepSize) < desiredBright_pct) currentBright_pct = desiredBright_pct; else currentBright_pct -= stepSize; } // else if else if (currentBright_pct < desiredBright_pct) { // is the difference between the two less than one step? if ( (currentBright_pct+stepSize) > desiredBright_pct) currentBright_pct = desiredBright_pct; else currentBright_pct += stepSize; } // else if SetPWMDutyCycle(mapPctBrighttoPWM(currentBright_pct)); return; } // stepBrightness void timerISR(void) { float lux; float pctDiff; stepBrightness(); if (lightReadingCounter) lightReadingCounter--; else { lightReadingCounter = 20; // 2 second delay lux = getLightLevel(); desiredBright_pct = getPctBrightFromLuxReading(lux); pctDiff = abs(desiredBright_pct - currentBright_pct); stepSize = (pctDiff <= 0.01) ? 0.01:pctDiff/10; } // else ClearInterruptFlag(); } // timerISR