[En-Nut-Discussion] TWI interrupts on AT91SAM7x256 and Ethernut 4.6.5/4.8.0

[Ulrich Prinz]

Hi Ajit! 
 
I implemented your patches in my local checkout of latest 4.9.x version. I 
investigate on TwMasterTransact problems too.  
As far as I can see, this function works well as long as you don't give a 
timout value. If you do so, TwMasterTransact will send given data out but 
does not continue to receive data if there is a number given for rxlen. 
 
Example: 
 
uint8_t PCA_Register = 0;  // Register inside I2C chip for its port 0 
uint8_t PCA_Keys;          // There are pushubuttons at port 0 
 
TwMasterTransact( PCA9555_ADDR, &PCA_Register, 1, %PCA_Keys, 1, 50); 
 
On the I2C bus I can see: 
<ST>0x23, 0x00<SP> 
 
Now I call it like this: 
TwMasterTransact( PCA9555_ADDR, &PCA_Register, 1, %PCA_Keys, 1, 
NUT_WAIT_INFINITE); 
And I see: 
<ST>0x23, 0x00<SP><ST>0x27, 0xkk<SP> 
 
where kk depends on the pressed buttons. 
 
So there is a problem inside the timeout handling of the I2C. 
 
I am not convinced about not keeping up TxMasterRegRead(). This funktion 
might speed up I2C as it handles registers inside target chips itself 
wihtout multiple transfers. But I have to read through the atmel bug lists 
carefully before making a decision  in that. 
 
Best regards, Ulrich 
 
On Fri, 3 Apr 2009 21:06:19 +0530 (IST), "Ajit Narayanan" 
<ajitn at inventionlabs.in> wrote: 
> Hi Harald/Ole, 
>  
> I made some progress on this bug. It looks like there are a few issues in 
> at91_twi.c related to the TWI errata of AT91SAM7x256 (41.4.9.1) which 
says 
> The value of CLDIV x 2^CKDIV must be less than or equal to 8191, the 
value 
> of CHDIV x 2^CKDIV must be less than or equal to 8191. 
>  
> For a client bitrate of 2400, this is not possible; we need a faster 
> bitrate. This can be changed in TwInit(). I changed it to 4800. 
>  
> The return value of the SETSPEED IOCtl is not being checked; this would 
> have caught the bug earlier: 
>  
> -   TwIOCtl(TWI_SETSPEED, &speed) 
> +   if( TwIOCtl(TWI_SETSPEED, &speed) ) { 
> +   return -1; 
> +   } 
>  
> Also, the check in the IOCtl (line 344) is incorrect: 
> -       if (cldiv * (2 << ckdiv) > 8191) { 
> +       if (cldiv * (1 << ckdiv) > 8191) { 
>  
> The bad news is, with all of the above, my application still doesn't work 
> :-(. But when I check with a scope, I see that at least master 
> transactions are initiated now. If someone with a Calypso board could 
give 
> it a shot and let me know, that would be great. 
>  
> It is still a mystery to me why this works with older Nut/OS versions. 
>  
>  
> -Ajit 
>  
>  
>> Ole Reinhardt wrote: 
>> 
>>> Ok, I had it just running with a client, but the above bug is realy a 
>>> bug :) 
>> 
>> On a SAM7X? May be there's a difference among MCUs. 
>> 
>> 
>>> I'll test it here any further if I get a I2C device connected to my 
>>> olimex board. Until then you might add a hint to the configurator 
option 
>>> not to use this code right now... 
>> 
>> No hurry. 
>> 
>> Unfortunately here is a second problem. Both, the hardware TWI as well 
>> as the bit banging version are added to the libs. It seems they are 
>> added by random, depending on the sequence of the referrers. 
>> 
>> As a temporary workaround one might copy twbbif.c to the application 
>> directory and add it to the Makefile. 
>> 
>> Harald 
>> 
>> 
>> _______________________________________________ 
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>> 
>  
>  
>  
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