2011-01-19 06:02:35 Query regd ad5624r_spi.c operation. Is it jitter free?

Ashish Gupta (INDIA)

Message: 97550

Hi,

We have a custom BF527 based processor platform and are curerntly selecting suiatble DAC chips for interfacing with Blackfin. We are considering the AD5664R DAC and wanted to enquire about the performance of the IIO framework driver currently in staging.

1. Is this driver's performance jitter free for sending out a waveform

Specifically I wanted to know that since ad5624r_spi.c's "ad5624r_spi_write" function seems to do a single sample write to the dual channel DAC, can it be used to send out a 100 samples waveform with jitter free performance?

Generally if there was DMA write that takes care of transferring full 100 samples of data without processor intervention and thus without latency, one would assume it would be jitter free. But since this driver's write seems to be a single write, will there be an unknown variable delay each time this function is called while sending out a 100 samples waveform (for example)??

2. If this driver cannot be used for jitter free performance, what is the best way to interface AD5664R to ADSP-BF527 in order to get jitter free performance for generating fairly continuous waveforms

Regards

Ashish

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2011-01-19 06:58:04 Query regd ad5624r_spi.c operation. Is it jitterfree?

Michael Hennerich (GERMANY)

Message: 97551 The IIO DAC drivers are not jitter free. If you need something

without jitter you have to use DMA in either SPI_MODE_0 or SPI_MODE_2.

- Where Blackfin SPI controller controls the SPI Slave select.

Care needs to be taken when selecting the DAC. For example the AD5624 requires

a 24-bit command word, and the slave select needs to be inactive after each sample.

This won't work in DMA mode!

- Since DMA only supports 8 or 16-bit transfers.

Therefore select one with a 16-bit command word.

Then you can use the spidev deriver with DMA enabled.

-Michael

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2011-01-19 14:32:11 Re: Query regd ad5624r_spi.c operation. Is it jitterfree?

Ashish Gupta (INDIA)

Message: 97552

Thanks Michael.

What would you say about using the SPORT + DMA for interfacing with DACs like AD5624. Since the SPORT is pretty flexible, is it possible to use SPORT frame sync signal as DAC's chip select and use it with DMA for jitter free performance?

Regards

Ashish

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2011-01-19 14:34:29 Re: Query regd ad5624r_spi.c operation. Is it jitterfree?

Ashish Gupta (INDIA)

Message: 97553

assuming we'll have to write a new custom driver for AD5624 that uses the SPORT + DMA.

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2011-01-20 03:31:05 Re: Query regd ad5624r_spi.c operation. Is itjitterfree?

Michael Hennerich (GERMANY)

Message: 97567 >

That should work!