Avalon Streaming simple example

Hi,

Many thanks for your reply. I am currently developing an autonomous data acquisition vehicle for oil and gas pipelines. We have nearly 300 analog sensors which ADC modules control them. Every second I should collect nearly 1MB of data which all are in packets and serially is being transferred to the FPGA. I collect this data and write them to CF in FAT32 format or send it through Ethernet. I implement some templates which write data into DDR RAM directly. This will avid processor to access ram for a while. There is an option which I can either implement another Ram or processor. However, power consumption on this system is very critical and I don’t want to implement extra devices. As data from ADC to RAM are serial and are in packets so I think I can use the Avalon streaming for achieving higher performance. So you are right. I want to read data serially from ADCs and buffer it somewhere. I need more reliable algorithms for that. I was wondering if you give me something to start with as I have never used Avalon streaming before. For Ethernet I am not using the Avalon streaming either as I am using my own IP. If I am able to use Avalon streaming so I can increase the TCP/IP stack performance.

Thanks,

Aidin.

:)

I think you want to use a DMA that accepts streaming data and writes it to memory which can then be sent later to flash or over Ethernet. There is a scatter-gather DMA that comes installed with the IP suite that gets used for various things like feeding streaming video to the screen or moving Ethernet packets back and forth in various designs that are installed with the Nios II EDS or on the Altera Nios II design examples page: http://www.altera.com/support/examples/nios2/exm-nios2.html

Here is an alternative SGDMA that you might find suites your needs better called the modular SGDMA: http://www.altera.com/support/examples/nios2/exm-modular-scatter-gather-dma.html

Here is an example of how I'm using it to implement dirt simple frame buffering to a streaming video pipeline: http://www.nioswiki.com/exampledesigns/modular_sgdma_video_frame_buffer

Streaming is a really simple standard to use especially if you have no 'ready latency' Most of the time when I use streaming I use only three signals:

data (payload data)

ready (tells the data source that the sink is ready for data)

valid (tells the data sink that the source is sending valid data)

Data flows from the source to the sink in only one direction. Assuming that there is no ready latency then the handshaking is literally 'valid == 1' and 'ready == 1' --> move data. In other words the source says "here's some data" and the sink says "I'm ready for some data", when that case occurs the data moves from the source to the sink and the next 1+ cycles this all starts again. Ready latency makes things a little more complicated and it's intended to factor in latency into the handshake. You can read more about it here: http://www.altera.com/literature/manual/mnl_avalon_spec.pdf

Since you are working with ADC you will probably use FIFOs to provide buffering so if the FIFO is configured for lookahead mode then you shouldn't have any ready latency to deal with.

*edit: I forgot about these too, I think DMAs would be better for you but just in case: http://www.altera.com/support/examples/nios2/exm-avalon-mm.html

Hi guys;

I want to use SGDMA to buffer video streaming from a CVI, do you think that it is possible? I have an input of 1080P60. Please inform me if you have an idea about that.

thanks.

Rabie

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Streaming is a really simple standard to use especially if you have no 'ready latency' Most of the time when I use streaming I use only three signals:

data (payload data)

ready (tells the data source that the sink is ready for data)

valid (tells the data sink that the source is sending valid data)

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That's great to hear! So I it is fine if I ignore the other signals in general?

Thanks

It depends on what you need but usually that triplet of signals is all that's necessary. There are other signals in the Avalon-ST spec and depending on your needs you might need them:

error: If you have to transport error information in the data stream

channel: If you have to transport a channel number in the data stream (i.e. interleaved channels in the same physical stream of data)

sop/eop: If you have to denote the start and end of a packet in the stream (for example if you were transporting Ethernet packets this would be handy)

empty: If you need to denote unused symbols in the data stream. (for example if you were transporting 32-bit data of Ethernet packets you can use this to mark how many symbols are empty at the end of a packet if the packet isn't a multiple of four 8-bit symbols).

Technically you can have an Avalon-ST port with just the data port but in general streams usually don't transfer data every clock cycle or have to backpressure so that's why you typically include ready and valid. The Avalon-ST protocol is very flexible just like Avalon-MM so there are very few mandatory signals to include.

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Technically you can have an Avalon-ST port with just the data port but in general streams usually don't transfer data every clock cycle or have to backpressure so that's why you typically include ready and valid.

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Thanks for your response!

I just had one more question: how much data exactly is transferred each clock cycle? One symbol?