looking for skinnier version of Raspberry Pi

Need a Raspberry Pi that can take in data from a SPI input and store in on a FAT formatted SD card > 2Gbytes. Board with needs to be less than

2". Length doesn't matter SPI speeds are ~ 2Mbits/sec

TI dogbone black (or whatever it is called) is close but a little too wide. Thinking about using my belt sander. :)

A uart for monitoring the progress via a laptop would be useful as well.

Do you guys know of a trimmed down version of the Pi that has this minimum functionality that I don't have to write the FW from the ground up. I'd rather use something that has a bit of a OS on it to reduce the programing task. If there is something with canned source files to implement something like this and a free compiler I'd be interested as well.

thanks

Reply to
Mook Johnson
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Den onsdag den 6. november 2013 13.07.10 UTC+1 skrev Mook Johnson:

something like this:

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-Lasse

Reply to
Lasse Langwadt Christensen

The RasPI is way overkill for this purpose. On Ebay you can get ATMega based boards for less than $5. For more complex projects you may want to check the Elua project and its supported platforms.

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Also worth considering is Carambola 2 at
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Reply to
asdf

...

I'll be impressed if you can pull off SD, and FAT32, inside an ATmega, with enough bandwidth to spare for 2Mb SPI (assuming contiguous transfers, that's only 80 clock cycles (on a typical chip) to handle all the overhead, transferring each byte from SPI register to FAT32 to SD).

Not familiar with Elua or Carambola, can't comment there. I'd think something ARM would be nicely suited (say.. ST Discovery?), assuming the form factor can be addressed.

Tim

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Reply to
Tim Williams

n
,

Yes, you need a better one than Atmega. PIC32 can handle 20Mb/s SPI, with

80MHz clock and 1/4 I/O clock, for example. You also need plenty of memory buffer for FAT32 and SD. The SD card might be able to handle high burst d ata transfer, but you need to allow time for it to think (or busy mode).

I have a 2"x2" PIC32 board that can use a USB / microSD card. It can read and write FAT (don't remember if it can do FAT32) uSD. Limiting to 2" (eit her way) also limit the connectors you can place on the board. In most cas es, i end up wiring to external connectors or devices directly.

Reply to
edward.ming.lee

The LPCxpresso is nice, especially the 120 MHz LPC1769 version.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

On a sunny day (Wed, 6 Nov 2013 07:44:53 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

If you only need to log some data, a filesystem is not needed. In fact dd if=/dev/sdc >myfile or whatever works great, I use it all the time, even for BluRay and DVD.

Saves time overhead, reduces errors (FAT?? you must be kidding), Increaes available space too.

As to filesystems: all my memory sticks except the camera and phone SDcards are ext2 or higher,

And partitions, who needs partitions. :-)

Reply to
Jan Panteltje

This comes out to 250,000 bytes per second.

This works out to be ~488 sectors/blocks per second.

NO SD card will be able to keep up this rate.

If your trying to stream to an SD card, this will not work.

Good Luck

Reply to
hamilton

I'm pretty sure I spotted somewhere FAT routines for those small processors, but unfortunately I totally missed the 2Mb/sec requirement that would rule out them entirely. Ouch...

Reply to
asdf

Should look at Google Chromecast: there is at least some chance that it uses the same broadcom chip as Raspberry PI..

Maybe forget FAT formatting and start with pre-erased blocks..

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Reply to
Joseph H Allen

On a sunny day (Wed, 6 Nov 2013 18:00:59 +0000 (UTC)) it happened asdf wrote in : I'm pretty sure I spotted somewhere FAT routines for those small

He is wrong about that, a class C SDcard is 10 MByte/second write:

formatting link

You can buy those from many places, prices are good too.

Does it have to be FAT?

Reply to
Jan Panteltje

On a sunny day (Wed, 06 Nov 2013 18:59:58 GMT) it happened Jan Panteltje wrote in :

eeeh class 10 of course...

Reply to
Jan Panteltje

Doesn't matter.

SPI (one bit interface) on an SD card is slow.

Four bit interface with SD interface is four times faster (minimum).

Internally, the SPI interface does not use the functions SD interface uses.

Hamilton

Reply to
hamilton

formatting link

My own testing shown this similar results.

The SD card interface timing uses a 20MHZ clock, SPI is normally 1-2 MHZ max.

SPI can only read/write one sector/block at a time. SD can read/write multiple sectors/block at a time.

formatting link

Reply to
hamilton

gumstix?

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Reply to
Jasen Betts

Thanks for the replies guys.

Fat is not required. Just nice to finish the experiment, pull the SD card out and stick it in a SD card reader on a PC to pull and process.

Most likely I can find a SD card that can store all of the experiments so a dump to a PC via the USB on this Pi like board would be acceptable.

The answer is still not clear on SD or no SD for writing at 2Mbits/sec. Seeing some of the SD card read write test on a PC at least 10 - 100X that performance has been shown for high specification SD cards. I suppose the interface HW and processor would need to support that.

The data is a stream from some SPI ADCs. eight 16 bit samples scanned at

15k samp/sec. Data just needs to be stored in several files separated by event. There will be maybe 10 events and a total time of 2 hours. should fit in a 2gig but will use a 4 or 8 for margin.

Anyone still with major concerns that the SD card cant keep up with this rate?

Reply to
Mook Johnson

Is it OK to dedicate a PC to monitoring the experiment? If so, something like a Saleae Logic might do what you want.

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I used one to monitor a TTL-level serial bus; I used a cheap PC with their software to capture the raw data with no analysis, and then used a good PC with their software to decode it the raw data into bytes and export it for further work. The software has protocol analyzers that understand serial, SPI, I2C, and other things.

I'm not sure if the Saleae software can do this. It does have per- channel triggering but I don't know if you can make it start a new file based on a trigger.

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Reply to
mroberds

Let me re-phase it, is it OK to connect to a PC/labtop close-by? If so, yo u can hook up a fast micro with less storage and stream the data directly t o the PC/laptop. Since you said you can have UART monitor, why not a USB o r ethernet or something else to pipe the data.

You would need the micro to handle the A2Ds; so, a dumb passive device won' t work.

Reply to
edward.ming.lee

This is approximately equal to the beagalbone black:

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but is 1.3mm narrower

Reply to
David Eather

the board will be in a location where a PC cannot be laced within the reach of say RS485. This setup will be battery powered and remote.

Reply to
Mook Johnson

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