Block mode streaming with AD16 modules

dunsworth · Joined: 20 Aug 2008 Posts: 4 Location: Edinburgh, Scotland

I am attempting to use block mode streaming using two AD16 modules in a C++ .NET application using the Caliente DLL.

Everything works fine when I specify a power of two number of ADC's but I find that the buffered data coming from the ChicoPlus board cycles through the channels when a non power of two number of ADC's is selected. This makes it impossible to accurately retreive the data for a specified channel pair.

I can work around this issue but can I confirm that this is normal behaviour? Is there any way without using the Channeliser to stream 5 channels (3 ADC's) say?

All help appreciated.

jhenderson · Posted: Thu Aug 21, 2008 7:43 am Post subject: AD16 with ChicoPlus

The AD16 module stacks pairs of 16-bit A/Ds onto an internal 32-bit bus which is reach by ChicoPlus during each sequencer instruction fetch. As a consequence, only pairs of A/Ds may be enabled for streaming.

gmiller · Joined: 07 Mar 2006 Posts: 105 Location: Simi Valley, CA.

In order to increase speeds along the PCI bus all A/D readings on this card are in pairs. When you enable any one of the paired A/D the other is also enabled. The data in block mode with have the 32 bit pair in the transfer. You can throw out the unneeded data or just let it reside in the block.

If you specify an odd number of channels you will still pick up the pair. If you specify only channel 0, channel 2, channel 4, you will actually get 6 channels of data in the block. The same is true for 1,3,5.

If all channels are in order say channel 0,1,2, you will still get channel 3 but this is the only extra channel you will see.

By adding channels of DIO or FIFO port you will also get another 32 bits for each in the block as if they were another channel pair for each peripheral.

Respectfully Gary

dunsworth · Joined: 20 Aug 2008 Posts: 4 Location: Edinburgh, Scotland

Sorry, I think you misunderstood my question due to my misuse of the term ADC.

I know that only channel pairs may be used but I am finding that I can only retreive data when a power of two number of channel pairs are specified.

I use the following code to enable/disable a channel pair:

dunsworth · Joined: 20 Aug 2008 Posts: 4 Location: Edinburgh, Scotland

I have attached a diagram to help illustrate the buffer cycling problem.

TIA.

jhenderson · Posted: Thu Aug 21, 2008 9:40 am Post subject: Power-of-two buffer sizes

Since the Pool buffers must always be sized as a power-of-two number of bytes under Armada, the number of enabled device pairs must also be even or else events (acquisitions from all enabled device pairs) will span buffer boundaries. I suspect that is what you're seeing.

dunsworth · Joined: 20 Aug 2008 Posts: 4 Location: Edinburgh, Scotland

I could maybe understand Jim if the device pairs had to be even, but not powers of two. It is a fairly serious shortcoming when you have two AD16 modules, as I can have 8 channel pairs and 16 channel pairs but nothing in between.

jhenderson · Posted: Thu Aug 21, 2008 7:16 pm Post subject: Device count

I apologize, I didn't properly synthesize my response. What I meant to say is that the tally of enabled device pairs divided by four should be evenly divisible into the buffer size. Typically, this allows device counts of 1, 2, 4, 8, and 16 to fit evenly into a buffer.

If you can't live with this restriction, you must use the channel merging components or aggregate the events using custom code.