comment.c

//
    // VBG_ADJ
    // DO NOT WRITE THIS VALUE UNLESS IT IS FOR THE LiIon BATTERY CHARGING CODE!!!
    // DAS - Changed based on defect 13606. Value may change for a few microseconds. 
    //
    // ADJ_VAG
    // Set to one so that we can explicitly adjust the Vag (audio ground
    // voltage) by writing to the VAG_VAL field.
    //
    // VAG_VAL
    // Vdda is the Vdd for analog output. In the 3600, Vdda is directly
    // connected to Vddd, the Vdd for the digital section. So, if we lower
    // Vdd to reduce power consumption in the digital circuitry, we are also
    // lowering the high rail of the audio output.
    //
    // If we were using the entire voltage span from actual ground to Vdda,
    // then lowering Vddd would do two things: it would lower the volume,
    // and it would clip the highest voltages in the output signal. Since we
    // want power-conserving measures to have no effect on user experience,
    // we need to do something else.
    //
    // What we do here is to set Vag appropriately for the lowest possible
    // value of Vdda. That way, Vdda can fluctuate all it wants, and the
    // audio will remain undisturbed.
    //
    // The lowest voltage at which the digital hardware can function is
    // 1.35V. Vdda can never be lower. So, we can set Vag to
    //
    //     1.35V / 2  =  0.675V
    //
    // and be assured that the audio output will never be disturbed by
    // fluctuations in Vddd.
    //
    // VAG_VAL is a 4-bit field. A value of 0xf implies Vag = 1.00V. A value
    // of 0 implies a Vag = 0.625V. Each bit is a 25mV step.
    //
    //     0.675V - 0.625V  =  0.050V  =>  2 increments of 25mV each.
    //
    // NOTE: It is important to write the register in one step if LW_REF is
    // being set, because LW_REF will cause the VAG_VAL to be lowered by 1.25/1.6.
    //----------------------------------------------------------------------