On 7/14/2011 12:55 PM, Tom Marchant wrote:
On Thu, 14 Jul 2011 08:40:37 -0600, Steve Comstock wrote:
yes, there is some penalty
for AMODE switching.
What penalty is that, Steve? Do BASSM and BSM run significantly
slower than BASR/BALR and BR?
There is no way the processor can know in advance which bits will be on in a
branch target register, so its seems likely that the pipeline must be flushed
when 'surprise' AMODE switching occurs for pointer-defined linkage. However, if
the BASSM/BSM is executed frequently enough, it's also possible the branch
history/prediction logic in the processor can guess the right target AMODE a
significant percentage of the time to minimize such 'surprises'.
I would not expect this to be an issue at all with the SAMxx instructions.
--
Edward E Jaffe
Phoenix Software International, Inc
831 Parkview Drive North
El Segundo, CA 90245
310-338-0400 x318
[email protected]
http://www.phoenixsoftware.com/
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