Richard,
On Tue, 13 Oct 2015 14:12:24 -0700, Richard Cochran
<richardcoch...@gmail.com> wrote:
On Tue, Oct 13, 2015 at 09:15:51PM +0200, Thomas Gleixner wrote:
Can we at least have a explanation of how the firmware operates? How
are (ART,sys) pairs are generated, and how they are supposed to get
into the DSP?
I'll give it a try. The audio controller has a set of registers almost
exactly like those on the network device. The e1000e patch adds the
e1000e_phc_get_ts() function. It writes a register to start the
cross-timestamp process and some time later the hardware sets a bit
indicating that it's finished.
In the case of the network, the host polls for this bit to be set,
indicating the cross-timestamp registers have valid data. In the audio
DSP case, it is the DSP that's doing the polling and it can only poll once
per millisecond.
The transfers look like:
Host -PCI (write request) -> DSP
[Transaction started from host]
DSP -PCI (write to initiate)-> Audio controller
[Transaction started from DSP]
DSP <-PCI (read to poll status)- Audio Controller
[Transaction Complete from DSP perspective]
DSP <-PCI (read (ART,device) pair)- Audio Controller
DSP -PCI (write notification) -> Host
[Transaction complete from Host perspective]
Host <-PCI read (ART,device) pair- DSP
I hope this is helpful. Thanks.
Chris
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
