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Add a comment from my local HAL about what is actually going on here

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with these ADC DC Gain/Offset calibrations.

The whole idea is to calibrate a pair of ADCs to compensate for any
differences between them.

The AR5416 returns lots of garbage, so there's no need to do the
calibration there.

The AR9160 returns 0 for secondary ADCs when calibrating 2.4ghz 20mhz
modes. It returns valid data for the secondary ADCs when calibrating
2.4ghz HT/40 and any 5ghz mode.
This commit is contained in:
Adrian Chadd 2011-01-20 08:40:22 +00:00
parent bd97c52a22
commit 564e7aea54
1 changed files with 17 additions and 0 deletions
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17
sys/dev/ath/ath_hal/ar5416/ar5416_cal.c
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@ -40,6 +40,23 @@ static int16_t ar5416GetNf(struct ath_hal *, struct ieee80211_channel *);
/*
* Determine if calibration is supported by device and channel flags
*/
/*
* ADC GAIN/DC offset calibration is for calibrating two ADCs that
* are acting as one by interleaving incoming symbols. This isn't
* relevant for 2.4GHz 20MHz wide modes because, as far as I can tell,
* the secondary ADC is never enabled. It is enabled however for
* 5GHz modes.
*
* It hasn't been confirmed whether doing this calibration is needed
* at all in the above modes and/or whether it's actually harmful.
* So for now, let's leave it enabled and just remember to get
* confirmation that it needs to be clarified.
*
* See US Patent No: US 7,541,952 B1:
* " Method and Apparatus for Offset and Gain Compensation for
* Analog-to-Digital Converters."
*/
static OS_INLINE HAL_BOOL
ar5416IsCalSupp(struct ath_hal *ah, const struct ieee80211_channel *chan,
HAL_CAL_TYPE calType)