NiosII with Altera SDRAM controller performance

Hello,

I find 2 reasons not to use burst with NiosII and Altera SDRAM controller :

1) I think it is slower than using Arbitration share to 8 without burst. After looking at simulation, burst adapters inserted (because SDRAM doesn't accept burst) add 2 cycles to every access. With a bank & row hit, SDRAM (with my configuration) returns 8 words of data in 14 cycles, so in 16 cycles with burst on. Read and write command arrive at SDRAM 2 cycle after leaving NiosII. Without burst, read and write arrive immediately at SDRAM, no latency added.

2) The size of design may increase due to burst adapter instantiated for each Nios II connection to slave. In a small sopc for Small hello world application (one NiosII/f with debug + sdram + JTAG uart) SOPC builder for instance seems to add 5 burst adapters.

But after doing again more carrefully simulation with burst while leaving arbitration share to default value 1, simultaneous access are not scattered. So speed it is better than without burst enable in this case. The benefit is so balanced between 2 cycles added to each 32byte transaction and simultaneous accesses not scattered. The result may depend of actual application...

Using no burst and arbitration share to 8 gives best result in all domains : no latency added, simultaneoeus accesses not scattered and no extra logic added...

Attached is 3 simulations of small hello world application : 1=> no burst with arbitration share to 1 defulat, 2=>burst 3=> no burst with arbitration share to 8. There are not a lot of accesses, but I think it show the difference. The faster execution is without burst but with arbitration share set to 8. Time is measured from end of SDRAM configuration to end of hello world message display. 1=> 80.52us, 2=> 80.32us, 3=>78.82us.

I am also a bit concerned with the recommendation of ALTERA you quoted: ALTERA seems to advice to design burst capable slave especially in the case of SDRAM controller, but its own made SDRAM controller doesn't implement burst itself ? That said, I love SOPC builder, it is actually a great tool to build system, and I just want to take the best of it :).

Michel