Is AHB Data Bus Size Programmable

[C4Cheema]

Hi
I have question about AHB data bus size
Can we change it at run time?
In my project I have two data flow for Camera IP Camera to Internal Memory (32 bit) and Camera to external memory (16 bit)
Camera IP is AHB compliant but I did not found any register through which I can program AHB Data Bus at running
By default output data is 32 bit
Do I need to change RTL to convert it into 16 bit or is there any other solution
Thanks in Advance
Bye

 

[ljxpjpjljx]

I think the size is fixed!

 

[pheobe]

I think there is size interface determining the transfer size, i.e. HSIZE

Hi
I have question about AHB data bus size
Can we change it at run time?
In my project I have two data flow for Camera IP Camera to Internal Memory (32 bit) and Camera to external memory (16 bit)
Camera IP is AHB compliant but I did not found any register through which I can program AHB Data Bus at running
By default output data is 32 bit
Do I need to change RTL to convert it into 16 bit or is there any other solution
Thanks in Advance
Bye

 

[C4Cheema]

HSIZE point out size of the transfer that will be byte (8-bit), (16-bit) or word (32-bit) maximum 1024 bits

My question was if we are using 32 bit Data Bus can we change it to 16 or 8 bit at run time
And I agree with ljxpjpjljx that size is fixed

 

[jailu_vlsi]

The protocol allows for the AHB data bus to be 8, 16, 32, 64, 128, 256, 512 or
1024-bits wide.

We can't change the Bus size at run time.

 

[Riveywood]

The AHB specification allows systems to be built with databus widths up to 1024 bits, although in practice 32 or 64 bits are the only commonly seen widths. The HSIZE bus allows masters to specify the size of the transfer they want to do - you can still do 8 or 16 bit reads or writes on a wider bus.

**broken link removed**

If you have a slave with a narrower memory width than the main databus, the usual solution is to implement some kind of downsizer. If the master does a 32 bit read or write, you convert that into two 16-bit accesses internally, for example.

In the original poster's case, I would expect an AHB slave to be implemented which is an external memory interface slave - it converts AHB accesses into whatever protocol the 16 bit external memory uses. I doubt very much the external memory uses AHB itself.