I have flashed the latest OpenWRT firmware on my WRT3200ACM. It is working and I believe it has been flashed to partition 2. So my factory firmware is still on partition 1.
Now, I want to also put DDWRT firmware on this router, using the first (alternate) partition, replacing the WRT3200ACM Factory firmware with DD-WRT firmware, and keeping OpenWRT firmware on the other partition.
What flashing process should I go through to get DD-WRT on the other partition from the Openwrt (Luci or ssh) interfaces?
For example, should I just be uploading/using the ddwrt-linksys-wrt3200acm-webflash.bin
or should I be using the ddwrt factory-to-ddwrt.bin ?
Which DD-WRT firmware image is suitable.
Second, should I be using Luci to flash the DD-WRT image or should I be using ssh with the sysupgrade -n -v <image-name> command?
DD-WRT cannot be flashed using the OpenWrt sysupgrade function. And, almost certainly if you try to use the stock firmware (by booting from the other partition), the stock firmware will write DD-WRT into the partition currently occupied by OpenWrt, overwriting OpenWrt in the process.
I suspect what you will need to do is connect via the serial UART to enable a transfer directly into the partition you specify. This is not straightforward, though... you'll need to ask DD-WRT people how to do this.
I'm almost positive the partitions are traded at this point and what was 'partition 1' is re-designated as 2.
It is not set in concrete, it is fluid.
I'm going to agree with @psherman on these: he is a Guru.
You cannot flash from OpenWrt to DD-WRT but you may be able to flash it first, then to OpenWrt; ask them.
But to help understand Netgear dual partitions:
Whatever 'partition' is 'upgraded' is preserved; as it is, presumed, "known good" and becomes designated partition 2 or 'backup'.
I double checked and no. I described it correctly:
The partitions are swapped every 'upgrade'; OEM or Open Source.
Your factory partition has been redesignated as 'backup'.
If you were to, let's say, flash/upgrade OpenWrt right now, you would lose your OEM partition as your current "known good" partition would become 'backup'.
It rarely makes sense to change between router distributions regularly, as there is always quite a number of configurations involved (IP ranges, static DHCP leases, wireless, …) which a) each have different syntax and semantics, b) might still behave slightly differently and can't be exported/ imported among each other either (see a). So what is the actual problem you want to solve?
If you want to test OEM vs DD-WRT vs OpenWrt, I would suggest to retain the OEM partition for the time being - and to flash DD-WRT or OpenWrt from there, after another, but not at the same time. This sidesteps all (most) of the flashing issues between the various firmwares.
Yes, Linksys' wrt3200acm is probably a bit more cooperative than many other routers when it comes to restoring the OEM firmware (at least from OpenWrt, I have no experience with DD-WRT, nor actually with the wrt3200acm at all) - and there are various stages of fallbacks, that make this particular hardware rather resilient, but if you know that you want to tinker around before committing to a particular firmware, it's still easier to avoid issues than to find solutions.
If your intentions are different, you will have to do more research.