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Possible to share Grand Central SD or QSPI with external dev
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Possible to share Grand Central SD or QSPI with external dev

by jim_s on Tue Aug 13, 2019 8:26 am

I have process control application employing a serial display device, and am trying to reduce any latency associated with communication with the display. (A series of multiple serial commands must be sent to update the display, so even using a hardware UART ends up sucking up some time to send the multiple commands.) It might be helpful to quickly dump a data structure to the SD or QSPI, then have an external processor read that data at its leisure, updating the display out-of-band of the main processor. The on-board SD or QSPI seems a possible path to this, if it can be written by the Grand Central, then read by an external device. Is this possible?

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Re: Possible to share Grand Central SD or QSPI with external

by adafruit_support_mike on Tue Aug 13, 2019 11:19 pm

There are no connections for an external computer to read the SD card or QSPI Flash directly, but it's easy to write a sketch that dumps their content to a Serial connection, or to some other interface on the GPIO pins. You could load that code after you do the data collection.

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Re: Possible to share Grand Central SD or QSPI with external

by jim_s on Wed Aug 14, 2019 9:32 am

Ok, Thanks for clarifying the lack of external access to the SD and QSPI devices, Mike. I think if I try to go with this inter-system-interaction-through-memory approach, I'll probably try to use something like an SPI FRAM chip. I was just hoping I might be able to utilize something already on the board.

This is in regard to a live process control system - I hesitate to use the term 'real-time', as there's lots of implications, grand assumptions and baggage that comes along with it - but there's really no down-time or 'after data collection' period during which I can spend a chunk of time sending stuff to the display, as the next externally-triggered event might come up during that time, and I have to deal with that immediately. I haven't yet exhausted all of my options on managing this better through the standard loop/interrupt approach, but some 'free' inter-system memory exchange would have been a low-hanging fruit to look into.

Thanks for your help!

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Re: Possible to share Grand Central SD or QSPI with external

by adafruit_support_mike on Thu Aug 15, 2019 12:00 am

Gotcha.. let's call it 'continuous processing and analysis'. Using an external memory device would be a good choice in that setting.

In fact, you might want to use two, as a rolling buffer. The Grand Central can write data to one device, then when it's done, switch to the other. That way you can write to one and read the other without too many synchronization issues. Assuming your write speed allows for it, you can swap every few milliseconds to keep the data fresh.

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Please be positive and constructive with your questions and comments.