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CONFIG_BFIN_INS_LOWOVERHEAD: ins[bwl] low overhead, higher interrupt latency

General informations

The Linux kernel configuration item CONFIG_BFIN_INS_LOWOVERHEAD:

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Reads on the Blackfin are speculative. In Blackfin terms, this means they can be interrupted at any time (even after they have been issued on to the external bus), and re-issued after the interrupt occurs. For memory - this is not a big deal, since memory does not change if it sees a read.

If a FIFO is sitting on the end of the read, it will see two reads, when the core only sees one since the FIFO receives both the read which is cancelled (and not delivered to the core) and the one which is re-issued (which is delivered to the core).

To solve this, interrupts are turned off before reads occur to I/O space. This option controls which the overhead/latency of controlling interrupts during this time "n" turns interrupts off every read (higher overhead, but lower interrupt latency) "y" turns interrupts off every loop (low overhead, but longer interrupt latency)

default behavior is to leave this set to on (type "Y"). If you are experiencing interrupt latency issues, it is safe and OK to turn this off.



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