prevent write/write collision in on-chip True Dual Port Ram

You only have to worry about concurrent writes to the same memory cell.

Read up on Dekker's algorithm, and use it to get the required exclusive access.

Or just arrange the interface so that the code ensures that both cpus are never going to write to the same location at the same time.

I just found http://cs.stackexchange.com/questions/12621/understanding-petersons-and-dekkers-algorithms

The 'turn' location could be written concurrently by both cpus, but if you just test odd/even in the Peterson case that won't matter.