> > On Sun, 05 Dec 1999, you wrote:
> Conversely, you can achieve the same latency reduction by setting the
> latency timer to 16, without increasing your overheads there. (This isn't
> actually entirely true, as you may run into busmaster ping-pong with more
> than one in the system, but you'll get this with reduced DMA bursts as
> well.)
I should have summarised this by saying: Correct use of the latency
timer will shorten your DMA bursts for you when necessary, giving you the
best of both worlds. When it's safe to run a long burst, you will. When
you need to push a device off the bus, that will happen too.
And the obvious extension to the "worst case" calculation is that if you
have N master devices each with a latency timer of X, your worst-case
timing for CPU access to a device is (N * X) + (N * arb overhead), just
in case that wasn't clear.
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