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Although this device is not yet officially
supported, I've been trying to get it working following success reported by
others in an earlier thread. I've followed the instructions in the DVB wiki
entry for this device, and have succeeded in tuning the device using the patched
version of szap, and recording a transport stream (using cat
/dev/dvb/adapter0/dvr0 > recording.ts).
However, the transport stream shows up
discontinuity errors which manifest as glitches in the playback. From the stats
produced by TS Reader the rate of loss is typically around 1 packet in 700,
though it varies from run to run.
I realise the simplest explanation for this would
be a poor quality signal. However, the device performs flawlessly under Windows
XP in exactly the same hardware configuration (same computer, dish, and sat
feed) when tuned to the same channels. This seems to rule out signal quality as
a cause unless the linux driver does not configure the device's error correction
properly. Is there any possibility this could be the case ?
I've also tried running the linux configuration on
two different computers - an AMD X2 4600 with Asus M2NPV-VM mobo, and a Via
EPIA5000 system (with a PCI 5-port USB2.0 card). The same problem occurs on both
systems.
I'm using kernel version 2.6.18-2. I also have two
DVB-T USB adapters which work with the same software configuration with no
packet loss.
The channels I've tried are BBC 1 London and BBC
HD. Obviously, the data rate is much higher on the HD channel. I've
cross-checked with the XP configuration to make sure that the frequencies,
polarity, etc. are correct in the channels.conf file.
Note that during the BBC HD trial from Crystal
Palace I was able to record this channel from a DVB-T adapter without packet
loss even on the EPIA5000 (533 MHz Via Eden processor).
I'm unable to determine at what point in the
processing chain the packets are being lost. I temporarily inserted some checks
for continuity errors on a specific pid in the 'dvb_dmxdev_ts_callback' function
in dmxdev.c. This showed packets had already gone missing at this point in
the driver. I don't know my way around the code well enough to be able to pursue
it further. In particular, I can't tell whether the packets are being discarded
somewhere in the driver, or within the device itself. The only kind of errors
which I detect are continuity errors. Does the device filter out all packets in
error or does it pass them through to the driver with the appropriate error
flags set in the packet header ?
Has anybody succeeded in getting an error free
transport stream from this device ? If not, are there any ideas about where the
problem might be ?
Thanks,
John
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