Combining Multiple DM355's

Although this is certainly possible, you will need to write some software.  One potential solution would be to communicate from one DM355 to the other using message queue and only have one DM355 access HDD; this path may cost some DDR2 bandwidth, but it is probrably not too hard to implement.  If you want both DM355 to share HDD, then this would almost resemble a multiprocessor system and the Linux port provided with the DM355 DVSDK does not support this, hence you will need to write the appropriate software to support this sharing of resources (can get quite complex).

I think the easiest way to use two DM355s for a dual channel setup would be to have them running independently and communicating over a network medium of some sort, unfortunately since DM355 has no on board EMAC you would have to do this through other means, perhaps TCP/IP over USB. A second issue is the HDD, since the DM355 has no ATA interface you would have to have some external hardware to talk to a HDD. Typically most DM355 applications end up using either a SD card storage solution or a USB based storage solution which is one way you could communicate fairly simply with a true HDD.

The message queue option sounds promising - but you say there would be DDR2 bandwidth costs.

How would this limit me specifically?  Reduced frame rate, resolution?  I'm looking at an application of

possibly only recording 1 or 2 fps on both channels.  Would this make things easier?

I was thinking of using the USB solution via HDD.  But I wonder what would be involved in implementing a serial ATA interface - probably a lot more time and mental energy than I can spare.

Both, frame rate and resolution play into figuring out the DDR2 bandwidth ( Theoretical max of 1296 MB/sec); however, at two frame per second I do not see this as an issue (what resultion are you planning?).

Also, keep in mind that DDR2 to AEMIF (used for HDD, SD, MMC, NAND...) maximum bandwidth is 66 MB/sec (assumong 16-bit wide bus), but the actual bandwidth may be lower depending on the file system chosen (EXT2, EXT3, YFFS2...).  Again, at 2 fps, I do not see this as a major problem.

attaching HDD via USB seems like the easiest path (no additional software to be written) as in the case of trying to implement ATA interface via AEMIF in software.

Putting in a SATA interface would be a significant effort, from both a hardware and software perspective, as you would need an external SATA controller as well as driver software to operate it, if you went with a USB solution that would work out of the box (you can mount a USB HDD from the EVM).

As to the DDR2 bandwidth I am not sure exactly what Juan had in mind with the message queue, but I do not think we can support a shared DDR2 setup, the timing and layout restrictions are tight as it is so this just does not seem practical, I suppose you could have an asynchronous SRAM shared between the two devices on the AEMIF but this would also be a bit cumbersome to use.

We can use the USB on one of the DM355 in Host mode and put the other DM355 in Device mode.  With this USB based setup we can run inter DM355 communication stream for control.  The DM355 that acts as USB Host can also interface with a USB-SATA adapter to which a SATA HDD can be connected.

Probably we can use the DM355 which is acting as USB Device to do the brunt of DVR operations and it can transfer the contents to the DM355 as USB Host over USB link.  Once at the DM355 USB Host the data can be written to the SATA HDD media over USB.

swami's suggestion seems sensible.  What I had in mind was something along the lines of CMEM for sharing memory, but did not give the hardware connection needed for this enough thought; all things considered, I like the USB idea.