dev:ath_hal_4:radardetection:ar9001

The AR9130/AR9160 radar reports include much more information than the previous generation.

The PHY error length is now (at least) three bytes, with the following information (for a frame 'n' bytes in length):

optional FFT payloads, if the pulse is long enough
byte n-3: Pulse length in the primary channel
byte n-2: Pulse length in the extension channel
byte n-1: flags

Flags contains:

0x01: Pulse in primary channel
0x02: Pulse in extension channel
0x04: “Early extension event” found (TBD: more explanation)

The stronger of the RSSIs in the primary and extension channel should be used.

An optional FFT report is available for frames which meet a certain set of parameters. This is primarily designed to assist in chirp detection, where a radar pulse moves in frequency over time. These pulses are normally detected as long pulses (45-90 uS).

Each FFT sample corresponds to a 3.2uS window (40MHz/80MHz clock) or 2.9uS window (44MHz/88MHz clock).

HT20:

Byte	Bit field	Description
0	[3:0]:	bin -28 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin -27 {bitmap, quantized magnitude[2:0]}
1	[3:0]:	bin -26 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin -25 {bitmap, quantized magnitude[2:0]}
2 - 25		…
26	[3:0]:	bin 24 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin 25 {bitmap, quantized magnitude[2:0]}
27	[3:0]:	bin 26 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin 27 {bitmap, quantized magnitude[2:0]}
28	[7:0]:	all bins {max_magnitude[1:0], bitmap_weight[5:0]}
29	[7:0]:	all bins max_magnitude[9:2]
30	[7:0]:	all bins {max_index[5:0], max_magnitude[11:10]}

Dynamic HT40 mode (regardless of whether the received data frames are HT20 or HT40; this is the mode the PHY is in):

Byte	Bitfield	Description
0	[3:0]:	bin -64 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin -63 {bitmap, quantized magnitude[2:0]}
1	[3:0]:	bin -62 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin -61 {bitmap, quantized magnitude[2:0]}
2 - 61		…
62	[3:0]:	bin 60 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin 61 {bitmap, quantized magnitude[2:0]}
63	[3:0]:	bin 62 {bitmap, quantized magnitude[2:0]}
	[7:4]:	bin 63 {bitmap, quantized magnitude[2:0]}
64	[7:0]:	lower bins {max_magnitude[1:0], bitmap_weight[5:0]}
65	[7:0]:	lower bins max_magnitude[9:2]
66	[7:0]:	lower bins {max_index[5:0], max_magnitude[11:10]}
67	[7:0]:	upper bins {max_magnitude[1:0], bitmap_weight[5:0]}
68	[7:0]:	upper bins max_magnitude[9:2]
69	[7:0]:	upper bins {max_index[5:0], max_magnitude[11:10]}

The radar FFT analysis provides a variety of information:

The max_magnitude is calculated, as the value of |I| + |Q|
the FFT bin index of the max_magnitude field is populated in max_index
for each bin, if the magitude is greater than a pre-programmed threshold (TODO: document this register field), the bit in the bitmap field is set;
the quantized magnitude is then calculated for all bins, calculated as floor(bin power * 8 / max_magnitude)

The FFT report data may be truncated if the incoming signal level drops before an FFT is completed. Thus, don't trust that the FFT data will be complete.
There are some known BB hangs with DFS on the AR9130/AR9160. The BB hang code in the ath_hal should detect it as a DFS BB hang and reset things. (TODO: check whether the chip needs to be “fixed” by going into another operational mode and bcak again, rather than just a straight reset.)
There are some corruption issues, where the MAC mis-classifies the larger PHY error frames as data frames and re-aligns some portion of the payload. This only affects frames with FFT payloads and not the short PHY error frames (3 bytes.)

Table of Contents

AR9130/AR9160 radar detection

Overview

PHY error frame format

FFT information

Notes / Limitations