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Connecting high sampling rate DAC and ADC to arduino DUE, timer consideration

I'm in the echopen association, our goal is to create a low cost, open source echographic probe. In order to do that, we use an arduino due for the first step. For doing acoustic imaging, we use ultrasonic transducer wich works at high frequency, typically 5 MHz. So, for our purpose we need to send and receive analogic signal at high frequencies. We want to connect a 80 Msps DAC and a 80 Msps ADC to the arduino due so we can generate and mesure analog signal up to 42 MHz. I have found here (http://www.instructables.com/id/Arduino-Timer-Interrupts/#step0) how to use arduino timer interrupts in order to send and receive data at 84 MHz. I haven't connect my converters for the moment, but I have preliminary questions. First, is the definition of the timer is the same for the arduino due (i.e. timer1 is a 16 bits timer) ? Morever, my ADC and DAC are 14 bits converters, can I tell to the arduino to sent only 14 bits digital signal ? Secondly, as we work at high frequencies we will have to send a lot of data from the microcontroller to a computer via the serial port. I have make a test and at 250000 bauds it takes nearly 0.5 second to transfer 4300*8 bits datas. It is to slow for our purpose, how can I do it faster ?

Answer*

I'm sorry, but by your description you are doomed to failure from the start.

The Arduino Due runs at 84MHz. That doesn't mean that it can communicate at 84MHz, only that it can process its instructions at around 84 million per second. 

In order for you to transmit or receive 80 million samples per second you have to be able to a) transmit sample words (14 bits) 80 million times per second, and b) process the information between each sample.

That means you are going to require a processor that operates considerably faster than 84MHz.

For instance, assuming you are using high speed synchronous serial communication (say, SPI) to transfer the data. For 16 bits of data (you won't get it to do just 14 bits using hardware and software would be way too slow) would require a transmission clock of (80000000 * 16) 1.28GHz.

If you're using a 16-bit parallel interface then you would only need an 80MHz communication clock to move the data around, but receiving that data and storing it somewhere and also processing it would require many many more instructions between each clock. Far more than the Due could perform. Certainly it's way way outside the scope of a timer interrupt.

I would suggest instead investigating systems that run in the high hundreds of Megahertz or even Gigahertz range. Maybe one of the newer "version 2" Raspberry Pi embedded computers may be suitable.

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I thought the arduino due can send digital data at each time clock... I have to find another way. Thank you for your answer

Dubois Jérôme
– Dubois Jérôme

2015年09月01日 09:09:46 +00:00
Commented Sep 1, 2015 at 9:09
The Due uses an ARM core. The ARM core is RISC. To, for example, get a byte from memory and place it on a port register takes minimum 4 instructions (load address, load data from address, load address, write data to address) and each instruction (load or store instruction) takes 1 clock cycle. That's in assembly. In C it becomes more, and as soon as you start looping you get even longer - condition tests, branches, incrementing values, etc - it may take upwards of 10 instructions with maybe 15 clock cycles for each access of the port. That would make about 5.6MHz maximum output.

Majenko
– Majenko

2015年09月01日 09:36:13 +00:00
Commented Sep 1, 2015 at 9:36
DMA might be able to do a bit better than the ARM core, but still the design seems farfetched. This is territory for an FPGA, or a very, very carefully chosen MCU. The pi is probably not a fit - the core may be fast, but that does not mean there is necessarily a suitable fast I/O interface.

Chris Stratton
– Chris Stratton

2015年12月01日 01:56:05 +00:00
Commented Dec 1, 2015 at 1:56

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