The uPSD is much more than a big 8051 and needs some configuration before playing with the IOs like you are trying to do. I think that this is what you miss in your tests, nothing to do with C/assembler.
Anyways, here is an example project for uPSD33xx in assembler which I will include it in the next version of RIDE:
It just increments a counter and writes the value of the counter on port A. (this is fine for the REva board. Maybe you'll have to modify it a little for the DK3300)
It includes the uPSD33xx startup, which is in two files, one assembler and one C file. You don't need to understand what the C file does, just include it in your project like in the example.
Then, there is the main.a51 file that you can modify for your own application.
And that's it.
Now, for using RIDE as a simple downloader, you simply need to uncheck the "debug" checkbox in the advanced debugging options.
This way, when you press "Ctrl-D", (that's two keys but still quite a short manipulation ) RIDE will just build the project and download it to the chip, but not start the debug. Then you just need to press the reset button on the board and the program starts.
I hope it helps.