On Sunday 17 June 2012 04:53:47 David Lynch Jr. wrote:

I am working on another AR9170 project. 
This essentially requires injecting broadcast packets
of specific size, frequency, ... at extremely precise
intervals.

Sounds pretty much like TDOA (and Gary). But anyway, if
you are just looking for a noise "pattern generator", you
might as well look into the "radar" branch of the carl9170
firmware.

I am trying to understand the data flow in the firmware. 

Initially I was looking to generate the frames in the firmware.

Well, there's "wlan_tx_fw" in wlan.c. Which can be used by the
firmware code to send out frames (Note: it's currently used to
sent BA when the device received a BAR from a HT peer)

Am I correct that the same struct dma_desc is being used by
both USB and the Radio?

Yes, it's a common data structure for lockless, vectored IO.

Each dma_desc points to a payload, for tx packets this is a struct
carl9170_tx_superframe, which must also be what the skb pointed to by 
void carl9170_usb_tx(struct ar9170 *ar, struct sk_buff *skb) is
sending ?

Yes. Altough, the (wlan) hardware will only cares about the 
ar9170_tx_frame struct which is embedded in the superframe.
So, the carl9170_tx_superdesc is "hidden" by wlan_tx before
the frame is sent down to the MAC's tx queue.
And likewise: unhide_super when the frame is given back to
the USB download queue.

Can I construct a carl9170_tx_superframe on the host side, with
something to allow me to identify it in handle_download in the firmware,
perform minor mangling of the contents, and repeatedly transmit it at
fixed intervals using wlan_tx() ?

Sure, the carl9170_tx_superdesc still has a unused u8 ["padding2"].
So, you can define your own set of flags and values right there. 
(Of course, you could also hijack rix and cnt - Note: this will work
if you only need to detect that the frames it needs to be handled
differently in handle_download since wlan_tx does override these
early on).

But if you need to repeatedly transmit frames, then the beaconing
mechanism might be worth a look. In theory it should be jitter
free since it is completely handled by the hardware.

Regards,
	Chr