[NTLUG:Discuss] RE: HDTV card for Linux

[Bryan J. Smith]

On Wed, 2004-09-08 at 02:51, Paul Ingendorf wrote:
> As for the IO constraints of a 33Mhz 32 bit interface I think that 125MB/s
> is plenty fast.

I'm not sure I agree.  0.125GBps is _ideal_.  Let's track the transfer.

One stream requires:  
- 3MBps from I/O to memory
- 3MBps from memory to storage

That is a sustained, continuous 6MBps -- plus overhead, setup, CPU,
etc... _per_ stream.  That's 12MBps for dual-streams.  And that's
_before_ we start talking overhead.

Let's put this into more of a "tangeable" form where sustained writes
are required.  For example, CD is 1.544MBps per "speed."  12MBps is
equivalent to 80x CD-R (6MBps is 40x).

So don't be surprised if you get dropped frames -- especially a
significant chunk of a second or two.

> The biggest problem you have on these architectures is memory io

Depends.  Some have embedded I/O controllers.

> and the lack of a DMA controller.

Again, depends.  A lot of uC/EuP systems have PIO/DMA programmable
lines.  UltraDMA and PCI Bus Mastering channels are _very_typical_ and
_standard_ peripherial nowdays.

In fact, more than one internal PCI bus is very common and cheap to do
in silicon.  So the ATA gets its own channel right in the stock
core+peripherial design.  About the only thing you can't put on the core
is the tuner or another EMF generating ADC/DAC (although multiple-dies
are now coming back to do just that -- but would drive costs up).  So
the tuner would get the external PCI runs -- so it should be a separate
PCI channel.

> They are still adequate though and in consumer electronics adequate is
> perfect, it means your not wasting money on something that does more
> than what it is intended to do.

Until PCI-Express comes out, I agree.  It's not worth the cost to get
0.5GBps+ PCI/PCI-X.

> Bringing me somewhat to your conclusion that with a consumer device
> like most of the PVRs you can buy today you will not see them supporting
> HDTV in their current incarnations.

Correct.  Although the LG HDTV ASTC/PVR has an IBM PowerPC 405 in it. 
But it won't let you watch and record independently -- single
input-only.

> There are a few HDPVRs on the market I don't know anything about them
> other than they do exist.

After just getting my first DirecTiVO a couple of weeks ago, I'm holding
off on HDTV this year because I'm waiting for them to mature.  I'm also
hoping the LCD _projection_ (not the LCD/Plasma, but LCD _projection_)
TVs break $2K by fall of next year.


-- 
Bryan J. Smith                                  b.j.smith at ieee.org 
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