ETPU - Shifting CBPA and CBPAE

[mertk]

Hello @davidtosenovjan and @johndiener,

I am working on AN4907 application on a development board.The memory processes with CBPAE is confusing my mind. 

Here the code block is: 

And here the resulting values of CBPA ve CBPAE:

How CBPAE gets 0xC3FCC3E0? I think it must gets 0xC3FC93E0 because of the result of the arithmetic process of 0x4000 >> 2 is 0x1000.

Same thing is occuring while writing to channel parameters. 0x249F0 value is written into ptr_untCPBAE + 0x14 not ptr_untCPBAE + 0x5. 

Is it normal?

Best regards,

Mert.

[mertk]

Hello John, 

Yes, your assume is correct. Data type of ptr_untCPBAE is uint32_t*. Now, I understand what I missing when I see your answer. This is pointer arithmetic.

Thank you for your helps.  

Best regards,

Mert.

[johndiener · Accepted solution]

Hello Mert,

It isn't shown in your code snippet, but I assume the type of 'ptr_untCPBAE' is 'int32_t*' (or 'uint32_t*') - this means when 0x1000 element steps are added to it, this transforms to a byte address offset of 0x4000 (sizeof int32_t is 4 bytes).

The last line of code displays similar behavior with converting a byte offset to a word offset by shifting right by 2 bits. It also uses an eTPU 24-bit address offset of 0x15 and converts it to a host-side byte address offset by subtracting 1 - this is typical of host code interacting with 24-bit data in the eTPU memory.  Note that it would probably be better if the constant 0x15 was represented by an address offset macro generated out of the eTPU tools.