[RFC] hostapd: allow configuring driver to VHT

Johannes Berg johannes at sipsolutions.net
Wed Nov 21 04:01:03 EST 2012


On Wed, 2012-11-21 at 14:13 +0530, Mahesh Palivela wrote:

> > +	if (data.vht_enabled) switch (vht_oper_chwidth) {
> > +	case 0:
> > +		if (center_segment1)
> > +			return -1;
> > +		if (5000 + center_segment0 * 5 != data.center_freq1)
> > +			return -1;
> > +		break;
> 
> instead of case 0, 1 etc, can you define names? can we have name for 5000?

Yeah, I guess I should do that.

> > +	case 1:
> > +		data.bandwidth = 80;
> > +		if (vht_oper_chwidth == 1 && center_segment1)
> > +			return -1;
> > +		if (vht_oper_chwidth == 3 && !center_segment1)
> > +			return -1;
> > +		if (!sec_channel_offset)
> > +			return -1;
> > +		/* primary 40 part must match the HT configuration */
> > +		tmp = (30 + freq - 5000 - center_segment0 * 5)/20;
> > +		tmp /= 2;
> > +		if (data.center_freq1 != 5000 +
> > +					 center_segment0 * 5 - 20 + 40 * tmp)
> > +			return -1;
> > +		data.center_freq1 = 5000 + center_segment0 * 5;
> > +		break;
> > +	case 2:
> > +		data.bandwidth = 160;
> > +		if (center_segment1)
> > +			return -1;
> > +		if (!sec_channel_offset)
> > +			return -1;
> > +		/* primary 40 part must match the HT configuration */
> > +		tmp = (70 + freq - 5000 - center_segment0 * 5)/20;
> > +		tmp /= 2;
> > +		if (data.center_freq1 != 5000 +
> > +					 center_segment0 * 5 - 60 + 40 * tmp)
> > +			return -1;
> 
> Sorry, I couldn't understand your arithmetic. Can you explain with example?

Oh, well, it's a little tricky, I had to draw a diagram:

Imagine each - is 5 MHz, so this is a 160 MHz channel, split into the 20
MHz subchannels:

|----|----|----|----|----|----|----|----|

Now each one of these could be the primary 20 MHz channel, which has the
center freq "freq" (in the code.)

center_segment0 points to the middle of the whole thing, so
	freq - (center_segment0 *5+5000)
will be -70, -50, -30, -10, 10, 30, 50, 70

Adding 70 will lead to 0, 20, 40, ..., 140
Divide by 20 will give us 0,...,7
Divide by 2 will give 0 ... 3, mapping 0,1->0, 2,3->1 etc.

data.center_freq1 is the center of the primary 40 MHz channel (as
calculated by the HT information, not VHT)

Now VHT must match this and given the 0..3 index we can calculate what
on the VHT side is the primary 40 MHz channel's center frequency --
which is the 160 MHz channel's center freq, minus 60, plus 40 * the
index.

Yeah, it's tricky ... This is vaguely based on pages 193-195 in the VHT
draft (formulas 22-1 through 22-7 and table 22-7)

johannes



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