Regarding digitalRead in bonescript

[Vasilis Iliadis]

I am playing with GPIO and digitalRead in bonescript. I noticed that although digitalRead is fairly fast the callback function takes a while. I am asking the group if I should wait for the callback to be triggered or just calling digitalRead is enough!.

Thanks

[William Hermans]

How would you plan on getting the information back from digitalRead if not by using a javascript callback ?

Also, more information is needed. e.g. what is your program goal ?

On Mon, Jan 5, 2015 at 2:38 PM, 'Vasilis Iliadis' via BeagleBoard <beagl...@googlegroups.com> wrote:

I am playing with GPIO and digitalRead in bonescript. I noticed that although digitalRead is fairly fast the callback function takes a while. I am asking the group if I should wait for the callback to be triggered or just calling digitalRead is enough!.

Thanks

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[Vasilis Iliadis]

The function digitalRead returns the value of the pin does it not? Basically what I ask is, if reading the return value of the digitalRead is enough, of should I capture the value of the pin via a callback function.
I am writing a small program where I interchange  the mode of a pin as input and output. I am having difficulties doing that.  I am a newbie in javascript, but I am wondering if that is possible at all.
Thanks in advance

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[William Hermans]

The function digitalRead returns the value of the pin does it not?

This I do not know first hand as I have never used bonescript. What I can say is that typically, when calling an executable directly from Nodejs ( which is what bonescript uses - Nodejs ), you need to use a callback to capture the output of that executable *if* you wish to use that value from within the script.

What I do imagine, as far as how bonescript works. Is that it directly calls an executable of some sort ( custom, or Linux command ), which then returns a value depending on which mode the pin is set as. Jason Kridner should know for sure since he wrote the library, and I could be wrong. I never really examined his code all that well, before I decided it was not for me.

Basically what I ask is, if reading the return value of the digitalRead is enough, of should I capture the value of the pin via a callback function.

 Ok, so if bonescript does in fact return a value, and if correct ( without a callback ), then there should be no problem. You could / should test the value to make sure it is correct though.

I am writing a small program where I interchange  the mode of a pin as input and output. I am having difficulties doing that.  I am a newbie in javascript, but I am wondering if that is possible at all.
Thanks in advance

I have read on these groups from various people that using a single pin ( GPIO - read / write ) is possible. However, I am left wondering in which case that would be useful. Whatever the case, digitalRead would only work when the pin is configured as GPIO -> IN.

Two ways I *think* you may be able to do this is using . . .

https://github.com/cdsteinkuehler/beaglebone-universal-io - This would be slow-ish, but you could call config-pin directly from Nodejs.

or by using pin(s) the PRU's can switch modes for fast. For something like say a buffer<->external memory. This way would also be far more complex, but should be vastly faster than using universal-io.

[William Hermans]

or by using pin(s) the PRU's can switch modes for fast. For something like say a buffer<->external memory. This way would also be far more complex, but should be vastly faster than using universal-io.

SO what I mean by being far more complex. Is that you would have to write an external Linux binary, that would  communicate with the PRU(s). Then, you would also need to write code for the PRU(s), so the programmable real time unit(s) could communicate with your Linux binary.

Typically, I would think this would be fairly useless, unless done for demonstration purposes. As the PRUs are really meant for high speed "applications", where speed is paramount - to a point ( 200Mhz ). Adding Linux to the mix alone would slow things down considerably, let alone Nodejs. As non real time Linux flavors only have around a 10ms timing resolution, and sometimes it can be far higher ( 100ms + ).

Anyway, probably moot for your case anyhow . . .

[Vasilis Iliadis]

First of all thank you very much for your valuable input. I think that your suggested method using the PRUs is what I need. In my application I need high speed data transfers using the gpios. I have to read/write a nand flash chip that are several Gbits of memory. For the same reason I need to utilize  8 pins as bidirectional input and output ( most nand flash chips use 8 pins for both address,command and data transfer). Now I just have to understand how PRUs work...:) I will check the net but if you have any tutorials on this please do tell. Again thank you very much.

[William Hermans]

Well, I know of nothing that you could not find via a search engine and "beaglebone black PRU" as I've done myself in the semi recent past. I'd shoot you some bookmarks, but I just got a new laptop in today that is a fresh install, and I'm trying to get that running . . . Everything I found though was by googling the above mentioned keywords. SO you should not find it too hard to find it all yourself.

[William Hermans]

Also, I am not sure if this would be useful for your case, but I talked with a person about a year ago about he GPMC on board. Just from memory, I recall this person telling me that 40MB/s throughput would not be much of a problem using this. However, I know less about the GPMC, than I do about the PRUs. Which is to say not a whole lot.

It may however be something worth looking into and as I recall you can access the GPMC through the PRU's . . .which possibly I am remembering wrongly, but still worth a look.