Avalon-MM-Slave address alignment

[Altera_Forum]

Hi All 

 I have aquestion regarding the address alignment of a an-MM slave.  My MM-Save has an avs_readdata and avs_writedata port each 512 bit wide. Now I'm trying to write the custom pripheral driver for the NIOSII. There I have to asign the correct address for read and write data but which comes first?  IOWR(base,0,data) IORD(base,513)   or vice versa?  Thank you for your answer!  Ben

[Altera_Forum]

Since the Nios can only do 32bit Avalon master cycles, you really don't want a 512bit wide slave. 

You'll only get a bus width adapter that will assert the revelant byte enables for the address. It is probably much better to write a 32bit slave.  I'm not sure what your problem with IORD() and IOWR() is - they are just wrappers that generate ldio and stio instructions. As such their definitions aren't entirely useful. Most device driver writers use C structures to map device registers, it is much less error prone than using integer offsets.

[Altera_Forum]

Hi dsl 

 You're right, I now changed my Avalon MM slave Custom peripheral to us it with burst transfer. However, I don't know how the _regs.h file needs to look.  For example, how to I write my 32bit width data over the IOWR() makro on the right position of my 512bit wide slave avr_writedata? Do I need to set the bytenable or address bits? But how?  Thank you for your help

[Altera_Forum]

IIRC the Nios won't generate burst transfers either (except maybe for cache line transfers). 

So qsys will probably have added a burst adapter!  Personally I'd just define the correct values and ignore the Altera definitions - they just confuse things. qsys will show a base address for your slave of (say) 0x123000, fix this rather than letting qsys assign the addresses.  In your header file: #define MY_SLAVE_BASE 0x123000 struct { volatile unsigned int reg_0; .... } my_device registers; extern struct my_device *my_device;  In your source, and assuming you aren't using the MMU: struct my_device *my_device = (void *)(0x80000000 | MY_SLAVE_BASE);  Then you can access my_device->reg_0 the same as any other variable.  The fabric will convert the low address bits into byte enables for you. But note that the nios always does 32bit reads, char/short writes will assert the expected byte enables.

[Altera_Forum]

If I declare my struct like you stated above and I try to write to reg_0 with 

<CODE> my_device->reg_0 = 1;<\CODE> my NIOS stops working.  However, if I check the address in debug mode of my_device it's the right one.

[Altera_Forum]

Hi dsl 

I was following the thread with great interest since I'm struggeling with something very similar. Thanks for the enlightenment!   --- Quote Start ---   So qsys will probably have added a burst adapter!   --- Quote End ---   If this is the case, how can I force it to make the burstcount as big as the number of symbols to be read, in order to prevent having the burst divided into a bunch of smaller ones?  I'm trying to transfer a 512 Bit package using your mentioned cache-method. Thanks, Markus.

[Altera_Forum]

It is a long time since I've looked at the options. 

ISTR there being one to request the cache do bursts. But it won't generate bursts longer than a cache line. An alternate approach is to dual port an M9K block as tightly coupled data memory. That will give the nios the same access times as a data cache hit. You need to make sure the m9K block is set for OLD_DATA (which implies single clock mode).

[Altera_Forum]

thanks for your answer! 

  --- Quote Start ---   But it won't generate bursts longer than a cache line. .  --- Quote End ---   The cache line is defined as 32, but the Nios refuses to make bursts longer than 8. I'd be perfectly fine with a 32-wide burst. This applies to both read and write bursts. :(

[Altera_Forum]

Isn't a burst of 8 transfering 32 bytes?

[Altera_Forum]

Both avs_readdata and avs_writedata are 32 Bit wide, so in order to have my 512 Bit package delivered, a burst of 16 is needed (whereas a burst of 8 is only half the rent). Please correct me if I'm wrong..

[Altera_Forum]

--- Quote Start ---  Isn't a burst of 8 transfering 32 bytes?  --- Quote End ---    now I see your point, sorry! Your're right of course. But I need to transfer 64Byte.