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Registered: ‎03-16-2014

Spartan6 DDR AXI Datamover Throughput

Hi,

I am designing an embedded system. The custom board has

Spartan6 xc6slx16  csg225 -2

DDR 1 Memory with 256Mb x8 running with 200MHz clock

The microblaze software runs on BRAM inside the FPGA not on the DDR.

 

I have an AXI Datamover IP configured as seen below.

My axi clock is 100MHz.

I also have a custom IP that controls the Datamover sending commands throught the command interface.

I want to measure the throughput of datamover. My custom IP keeps m_axis_mm2s_tready always at high and send a single mm2s transfer command at a time.

What I observe is that the m_axis_mm2s_tvalid signal of the datamover is NOT continuously high during a burst but rather toggles at each clock cycle during a burst as seen below.

The burst duration (when m_axis_mm2s_tvalid asserted) is measured to be 1.28usec = 128clk cycles @ 100MHz.  Normally for a burst shoud take 64 cycles. But in my case it almost takes twice reducing the data throughput.

The datasheet specifies the throughput as ~390MBps but in this case the peak throughput is roughly 256Bytes / 1.28usec = 190MBps

Do you have any ideas why this happens?

Is it related to my settings? 

Can DDR RAM be the bottleneck?

 

Regards

 

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