Electronics > Projects, Designs, and Technical Stuff
DDR2 chip how slow can you go?
GeorgeOfTheJungle:
--- Quote from: JohanHoltby on August 30, 2019, 10:20:36 pm ---When I did look in to the Flash modules I noticed that I will need to replace the SD cards two times every year for a 128Gb SD card. And since this system will be deployed by an EMS overseas often I don't have the luxury of replacing SD cards. SO about 10 years of operation would be great.
--- End quote ---
16 MB/s are 16*3600*24*365/1024 ~= 500 TB/year IIANM. That's almost 250000/128 ~= 2000 full card rewrites/erases in six months. An SD card can really handle that much?
There are now 256 and 512GB cards. If you've got spare pins or SD card interfaces in the STMs perhaps you could devise a RAID-ish setup with more than one card.
Yansi:
Spare SDIO interfaces should not be required, SDIO I think supports multiple device interfacing. Never tried it though.
I still think this project is poorly thought out and the goal is not clear.
JohanHoltby:
--- Quote from: Yansi on September 01, 2019, 10:05:03 am ---I still think this project is poorly thought out and the goal is not clear.
--- End quote ---
Interested (with a true open mind, not aiming for protecting my darling) in what you think is the poor parts and do you have any suggestions? In the end I want this to be as a good product as it possible could be.
To give some more background:
Normally I get a limited test specification which are updated many times so there for I enjoy wokring with matrix based interface systems (TPs, instruments and PS on columns and they can be switched in by software to a number of shared rows e.g. PXI-2533) which enable only software updates as the product specification updates as long as the TPs stay in place.
However DUTs break and people make mistakes so debugging and safety is important. This leads to multiple reruns to find bugs and broken equipment in worst case. To avoid reruns I want an all seeing scope which can log all current and voltage going through the matrix. Whenever any thing breaks I want the matrix to trigger if e.g. a current is above set value and disconnect the switch.
Since the specifications is not set ahead of time I want to have it modular so that it will be able to connect and disconnect modules depending on specification changes. And since test systems is almost always one offs making custom PCBs are very costly in regards to labor cost.
Yansi with that background what would you suggest?
Yansi:
I am still quite confused, as what the design goal of your instrument should be. Have you posted a full definition of it? I do not follow the thread carefully, I may have missed. It even seems the design goal is changing throughout.
What I would like to see is something like this:
State the intention of the device, the typical end use (for us, who are not familiar for example with those PXI systems mentioned which)
State the desired electrical interfaces, bot inputs and outputs and its characteristics:
ie.: I need to record 32 analog voltage channels at 1Msps rate @12bit resolution and sample them simultaneously for whatever the reason. I need to record all channels for as long as 1 minute, and then read out the sampled values from the device through XYZ interface.
T3sl4co1l:
Why would you even consider an STM over, say, a multicore SOM, using USB or PCIe (and bridges, interfaces, FPGAs, etc. as needed) to concentrate data from the various peripherals?
Such a device also trivially(?) runs Linux, communicates over Ethernet, connects to the Internet, connects ordinary HID devices, HDMI or DVI or whatever monitors, etc. In short, a small PC with custom hardware attached.
Timing constraints for test equipment usually isn't terribly tight (i.e., on a similar scale as toggling relays), so the relatively poor timing of a multitasking OS is fine; real-time functionality is still available, with some difficulty (run as root? timing still subject to device drivers and hardware timing?), but preferably all hard real-time activity should be constrained to the peripherals themselves, and merely buffered data flows to the PC.
Tim
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