Lpc2000

---- Original Message ----
From: "croquettegnu" <croquettegnu@...>
To: <lpc2000@yahoogroups.com>
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