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

Altera_Forum · ‎08-12-2010

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：

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 · ‎08-12-2010

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 · ‎08-12-2010

OK,I understand, thank you