custom instructions

[Altera_Forum]

Is there an easy way to write custom instructions which read and write to SDRAM? 

 In particular, we're trying to make an compare-and-swap instruction in order to do multi-threading.  Also, though, this would be useful for matrix multiplication instructions and vector instructions as well.  Any pointers towards a simpler interface to SDRAM than directly banging on the SDRAM controller would be appreciated; in particular if there's any way to coordinate with load and store instructions (I presume that each one doesn't implement its own interface to sdram -- is there any way to reuse their interface?).  Thanks.

[Altera_Forum]

You'd have to interface with an SDRAM controller so it's not impossible, but I wouldn't want to try either. SDRAM needs a controller to talk to it due to the complexity of SDRAM in general. 

 I don't understand the idea you have all that well so I can't offer an alternative. I'm sure if someone gets this one they may have something else for you.

[Altera_Forum]

Basically, in order to do multi-threading safely and efficiently, you need to have some instruction which can read from a location in memory, do something to it, and write the result back to the same location in memory. The functions can vary -- add, decrement, compare and swap; it's not so important as being able to have an atomic load-operate-store instruction. 

 Also, one needs this for simd instructions like vector or matrix multiplications.