mdavister
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Doing something useful with the PI

Wed Sep 23, 2015 2:31 pm

A lot of what I've seen about the PI is on the order of "fun" or "neat" applications. I want to do something useful with a PI, moving data around and controlling some signals. Is it possible to get higher bandwidth I/O on a PI type computer? I'd like to be able to toggle some IO pins at least above 20 MHz, and be able to move data at about 11 MB/s from the outside world into the PI. Is this even possible? I have read through the specs a bit, and it appears the processor is quite capable, but the outside world is accessed through GPIO for the most part. Other processors are a great deal slower when running over GPIO.

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RaTTuS
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Re: Doing something useful with the PI

Wed Sep 23, 2015 2:38 pm

USB interface is USB2 480Mbps
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W. H. Heydt
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Re: Doing something useful with the PI

Wed Sep 23, 2015 3:29 pm

I do something very useful with a Pi. It's my "alarm clock".

mdavister
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Re: Doing something useful with the PI

Wed Sep 23, 2015 4:05 pm

While USB is a fast interface, I still need something to convert raw data into the USB format, manage the protocol and link etc. I need raw bit bangin' speed.

Tom_A
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Re: Doing something useful with the PI

Wed Sep 23, 2015 4:30 pm

W. H. Heydt wrote:I do something very useful with a Pi. It's my "alarm clock".
One of mine is media viewer, AirPrint server, music player, and announces the time on each hour.

W. H. Heydt
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Re: Doing something useful with the PI

Wed Sep 23, 2015 5:10 pm

Tom_A wrote:
W. H. Heydt wrote:I do something very useful with a Pi. It's my "alarm clock".
One of mine is media viewer, AirPrint server, music player, and announces the time on each hour.
If I were going to make it mark the hours (and I've considered it), I would have it do ships bells.

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mikronauts
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Re: Doing something useful with the PI

Wed Sep 23, 2015 5:16 pm

Short answer:

NO.

Longer answer:

1) Try the DMA mode in joan's pigpio library, you will need a large buffer, and you will need to move the bits around, but it may be possible.

2) Add a USB microcontroller to do the hard real time data gathering, and if it has high speed USB, have it send it to the Pi in batches

3) Pester the Raspberry Pi Foundation to release documentation on the "Secondary Memory Interface" which is available on the Model A+/B+/Pi2 40 pin GPIO connector, then we can all play with high speed I/O :)

I, and others, have asked for documentation, and the responses have been "maybe later"

I even tried to get docs from Broadcom, they told me to ask the Pi Foundation for it.
mdavister wrote:A lot of what I've seen about the PI is on the order of "fun" or "neat" applications. I want to do something useful with a PI, moving data around and controlling some signals. Is it possible to get higher bandwidth I/O on a PI type computer? I'd like to be able to toggle some IO pins at least above 20 MHz, and be able to move data at about 11 MB/s from the outside world into the PI. Is this even possible? I have read through the specs a bit, and it appears the processor is quite capable, but the outside world is accessed through GPIO for the most part. Other processors are a great deal slower when running over GPIO.
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PiGraham
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Re: Doing something useful with the PI

Wed Sep 23, 2015 5:50 pm

RaTTuS wrote:USB interface is USB2 480Mbps
That's the raw bitrate, but what sustained data rate can the Pi manage?
Remember that the network uses some of that bandwidth, either Ethernet or USB WiFi.

Here's a report of using a USB Gb Ethernet adaptor to get 27 MByte/s on a B+
I then purchased a TRENDnet USB 3.0 Gigabit adapter from Amazon to test on my Pi. After configuring the interface by editing /etc/network/interfaces and adding a line for the new eth1 adapter, I ran standard iperf benchmarks on all the interfaces and found the following results:
•Internal LAN (10/100): 94.4 Mbits/sec (11.8 MB/sec)
•USB 802.11n WiFi: 44.5 Mbits/sec (5.6 MB/sec)
•USB Gigabit LAN (10/100/1000): 222 Mbits/sec (27.8 MB/sec)

http://www.midwesternmac.com/blogs/jeff ... networking

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