Why is the maximum burst count 2 ** (AV_BURSTCOUNT_W-1)

[Altera_Forum]

In altera_avalon_mm_master_bfm, when the burst count is greater than 2 ** (AV_BURSTCOUNT_W-1), it will generate a warning. Suppose AV_BURSTCOUNT_W is 4, then the maximum burst count is 15 instead of 8, is this a bug in altera_avalon_mm_master_bfm ? 

 Here is the relevant code&#65306;   if (burst_count < 1) begin  $sformat(message,   "%m: Illegal Burst Count value: %0d - must be >= 1",  burst_count);  print(VERBOSITY_WARNING, message);  end else if (burst_count > 2**(AV_BURSTCOUNT_W-1)) begin  $sformat(message,   "%m: Illegal Burst Count value: %0d - must be <= %0d",  burst_count, 2**(AV_BURSTCOUNT_W-1));  print(VERBOSITY_WARNING, message);  end

[Altera_Forum]

The maximum burst count is 2**(N-1) because that is what Altera defined it to be in the avalon interface specifications (http://www.altera.com/literature/manual/mnl_avalon_spec.pdf). 

 This definition is somewhat arbitrary. I would guess Altera chose 2**(N-1) instead of (2**N) - 1 so that the max burst count is an even power of 2.  To guarantee compatibility between components, you need to adhere to the specification.

[Altera_Forum]

OK,I understand, thank you