Hello,
you have answered a post concerning the FAST I/O feature and told that
the FAST GPIO were on the local bus because this bus is the fastest on
the chip and so faster than the AHB bus
I would like to know the differences between these two busses because
as the ARM Core is a ARM7TDMI-S, you should be able to access directly
the AHB bus which for me was the fastest bus...
Thanks a lot!
Frederic
ARM7 Local Bus vs AHB
Started by ●April 7, 2006
Reply by ●April 7, 20062006-04-07
---- Original Message ----
From: "croquettegnu"
To:
Sent: Friday, April 07, 2006 10:54 AM
Subject: [lpc2000] ARM7 Local Bus vs AHB
> you have answered a post concerning the FAST I/O feature and told that
> the FAST GPIO were on the local bus because this bus is the fastest on
> the chip and so faster than the AHB bus
>
> I would like to know the differences between these two busses because
> as the ARM Core is a ARM7TDMI-S, you should be able to access directly
> the AHB bus which for me was the fastest bus...
The AHB bus is fast, but the local bus is faster.
Just tested this:
Accesses on the local bus (RAM, flash, fast GPIO) are done without
waitstates (except sometimes when MAM adds flash waitstates), so that a load
(LDR) takes three clocks, and a store (STR) takes two clocks.
Accesses to peripherals on the APB bus (timers, uarts, slow GPIO etc) are
done with five waitstates (with APBDIV=1) so that LDR and STR take 8 and 7
clocks respectively.
Accesses on the AHB bus (VIC registers) are done with one waitstate so that
LDR and STR take 4 and 3 clocks respectively.
Karl Olsen
From: "croquettegnu"
To:
Sent: Friday, April 07, 2006 10:54 AM
Subject: [lpc2000] ARM7 Local Bus vs AHB
> you have answered a post concerning the FAST I/O feature and told that
> the FAST GPIO were on the local bus because this bus is the fastest on
> the chip and so faster than the AHB bus
>
> I would like to know the differences between these two busses because
> as the ARM Core is a ARM7TDMI-S, you should be able to access directly
> the AHB bus which for me was the fastest bus...
The AHB bus is fast, but the local bus is faster.
Just tested this:
Accesses on the local bus (RAM, flash, fast GPIO) are done without
waitstates (except sometimes when MAM adds flash waitstates), so that a load
(LDR) takes three clocks, and a store (STR) takes two clocks.
Accesses to peripherals on the APB bus (timers, uarts, slow GPIO etc) are
done with five waitstates (with APBDIV=1) so that LDR and STR take 8 and 7
clocks respectively.
Accesses on the AHB bus (VIC registers) are done with one waitstate so that
LDR and STR take 4 and 3 clocks respectively.
Karl Olsen