Embedded system control loops and reading from daisy-chained ADCs

[Nicholas Kinar <n.kinar-/KKvz3x1pcI@public.gmane.org>]

Hello,

I am in the process of designing an embedded system that needs to read 
values over SPI from 5 daisy-chained ADCs.  The ADCs are the AD7685 from 
Analog Devices 
(http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7685/products/product.html).  
These are 16-bit ADC slave devices that are read over a SPI bus.  I 
would like to read these devices at a rate of 1 kHz.  I am using the ARM 
AT91SAM9RL processor.  This processor will run the Linux kernel.

To read values from these ADCs, the processor must first toggle a port 
pin (CNV) to initiate a conversion.  The processor needs to toggle the 
port pin at a rate of 1 kHz, perhaps using a high-resolution timer.  
After every conversion, the processor needs to lower a chip select pin 
and read data consisting of a (16 bit)(5) =  80-bit word.  The chip 
select pin then goes high.  I assume that the daisy-chained ADCs would 
appear to the kernel driver as a single SPI slave with MISO, MOSI, and 
\CS pins.  The only difference is the CNV pin that is needed to initiate 
a conversion.

After every conversion, the kernel driver needs to make a comparison (is 
the value from each ADC above or below a certain value).  The kernel 
driver needs to then select an SPI slave DAC (AD5621) or I2C slave DAC 
(AD5622) and update the voltage output of the DAC.

I need to read data from the ADC slaves at a rate of 1 kHz.  What is the 
best way to do this without introducing too much jitter, and is it 
possible to do this all with one kernel driver?

Nicholas


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