Re: Sending one byte transfers using SPI bus with linux-2.6.32

Re: Sending one byte transfers using SPI bus with linux-2.6.32

[Grant Likely]

Elvis Dowson <elvis.dowson-ee4meeAH724@public.gmane.org> wrote:

>Hi,
>I modified the spidev_test.c program and I find that when sending data,
>I have to specific a minimum transfer length of 2, for a message. 
>
>If I specify an array size of 1, no transfer takes place.

What backend spi master driver/device are you using?  Single byte transfers should work. It may be a bug/limitation of the driver.

g.

-- 
Sent from my Android phone with K-9 Mail. Please excuse my brevity.

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Re: Sending one byte transfers using SPI bus with linux-2.6.32

[Kevyn-Alexandre Paré]

Hi Elvis,

I have done some test without problem with spidev_test.c and was sending
tx[1].

Best Regards,

Kevyn-Alexandre Paré

On Fri, 2011-03-04 at 20:58 +0400, Elvis Dowson wrote:
> Elvis Dowson


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Re: Sending one byte transfers using SPI bus with linux-2.6.32

[Kevyn-Alexandre Paré]

Just to mention that I was with OMAP 3530
2.6.34 and know 2.6.36 (gumstix overo)

kap

On Fri, 2011-03-04 at 14:56 -0500, Kevyn-Alexandre Paré wrote:
> Just to mention that I was with OMAP 3530
> 2.6.34 and know 2.6.36 (gumstix overo)
> 
> kap 


------------------------------------------------------------------------------
What You Don't Know About Data Connectivity CAN Hurt You
This paper provides an overview of data connectivity, details
its effect on application quality, and explores various alternative
solutions. http://p.sf.net/sfu/progress-d2d
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Re: Sending one byte transfers using SPI bus with linux-2.6.32

[Kevyn-Alexandre Paré]

simply t[1] I reuse -s option just diff it with the original

http://pastebin.com/Ys6wMD1S

Did you try later version of kernel?

Kevyn-Alexandre Paré



On Sat, 2011-03-05 at 00:11 +0400, Elvis Dowson wrote:
> On Mar 4, 2011, at 11:58 PM, Kevyn-Alexandre Paré wrote:
> 
> > Just to mention that I was with OMAP 3530
> > 2.6.34 and know 2.6.36 (gumstix overo)
> 
> Ok, 2.6.32 didn't work for 1 byte transfers.
> 
> Do you have a sample code snippet that you can share, or was it just putting tx[1] and re-using the spidev_test.c example.
> 
> Elvis Dowson



------------------------------------------------------------------------------
What You Don't Know About Data Connectivity CAN Hurt You
This paper provides an overview of data connectivity, details
its effect on application quality, and explores various alternative
solutions. http://p.sf.net/sfu/progress-d2d
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Re: Sending one byte transfers using SPI bus with linux-2.6.32

[Kevyn-Alexandre Paré]

A simple git diff should have save us some time ;)

git diff v2.6.32 v2.6.36 -- spidev_test.c
warning: refname 'v2.6.32' is ambiguous.
diff --git a/Documentation/spi/spidev_test.c
b/Documentation/spi/spidev_test.c
index 10abd37..16feda9 100644
--- a/Documentation/spi/spidev_test.c
+++ b/Documentation/spi/spidev_test.c
@@ -58,7 +58,7 @@ static void transfer(int fd)
        };
 
        ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
-       if (ret == 1)
+       if (ret < 1)
                pabort("can't send spi message");
 
        for (ret = 0; ret < ARRAY_SIZE(tx); ret++) {

-- kap

On Sun, 2011-03-06 at 21:45 +0400, Elvis Dowson wrote:
> Hi,
>         The problem was in the spidev_test.c program itself, in linux-2.6.32.
> 
> After applying the following patch taken from linux-2.6.34, 1 byte transfers work.
> 
> http://git.kernel.org/?p=linux/kernel/git/longterm/linux-2.6.34.y.git;a=blobdiff;f=Documentation/spi/spidev_test.c;h=16feda9014692a87a4996bf51d759ab9e7500ee5;hp=10abd3773e49122aab0dfad27f7cb2c91b8d5d08;hb=95b1ed2ac7ffe3205afc6f5a20320fbdb984da92;hpb=dda04c7bcf58cb02ac796beb1cf483aa5277f2af
> 
> Elvis Dowson



------------------------------------------------------------------------------
What You Don't Know About Data Connectivity CAN Hurt You
This paper provides an overview of data connectivity, details
its effect on application quality, and explores various alternative
solutions. http://p.sf.net/sfu/progress-d2d