Lpc2000

Ok, I've been mulling over this for weeks now and I can't really 
come to a decision as to which chip I want to use.  They both seem 
like pretty good chips, with some slight benefits and detriments.  
I'm looking at making just a small generic basic system with 128x64 
LCD, RS232, USB, MMC and possibly MP3 support.

(Please correct me if I cam wrong on any of the following points)

The AT91SAM7S has DMA for all of it's peripherals, which is nice, 
but I'm not sure if it's really necessary for me.  The LPC2148 has 
an 8KB DMA'd buffer for USB, vs 384byte on AT91.  The LPC has a DAC, 
but it's only 10-bit so that's really not any use for MP3 output (or 
is it?).  The LPC also has 128-bit memory access, vs 32-bit for SAM, 
and I've heard that can be quite a nice little bonus for execution 
speed.  The LPC can go up to 512KB flash, vs 256KB for the AT91SAM7S 
series, but the AT91 goes up to 64KB RAM, vs only 40KB for LPC.  The 
LPC can run it's com port at almost any baud rate regardless of 
source clock, but the AT91 has a pretty good fractional divider 
which gives all usual baud rates anyway, and most of the unusual 
ones.  The AT91 doesn't require an external OSC, but I can't find 
out much info on the capabilities of the RTC (does it even have one?)

Or should I be considering a different set of chips altogether?  I 
like these SOC's because they're simple and low external component 
count.  I don't need massive code memory, or fast massive RAM memory 
(I can always hook up the RAM chips manually on the GPIO lines and 
page the data into RAM).  The USB is a great plus, so I think that 
these are the chips to go with...

As you can see there are a lot of factors.  Does anyone have any 
information or suggestions that can help me choose between the two?

Thanks a lot!

This is the best comparison I've seen of these popular families. I 
didn't see you mention Ethernet but maybe that's not a concern for you.

The AT91SAM7X256 should be out by now and that looks great - you might 
want to look at it.

One issue that concerns me: there's an open source downloader to 
program flash on Philips devices, but nothing like that exists for the 
Atmel devices yet. As I understand it (someone correct me if I'm 
wrong), there's no linux downloader (of any kind) for SAM-BA, and 
there's no commandline downloader for Windows. 

Commandline downloaders are convenient to use with various IDEs that 
don't have built-in JTAG support. An open source downloader gives us 
IDE authors a good example of how to integrate support for it into 
IDEs.

I didn't check to see if Atmel fully documented the SAM-BA API, but it 
seems like its closed. They also didn't seem to publish the API for 
their DLL either. Or maybe this stuff is documented somewhere, or 
maybe it will be soon. Atmel seems like a fairly open company so I'm a 
little confused about this.

However, it's also fair to point out that Philips does not support 
programming flash over USB at all (you could roll your own code, of 
course). but Atmel does (if you can make use of their Windows GUI 
program).

Eric

--- In lpc2000@yahoogroups.com, "Eric Engler" <englere.geo@y...> 
wrote:
> I didn't see you mention Ethernet.  The AT91SAM7X256 should be out
> by now and that looks great - you might want to look at it.

I mentioned that in my original post.  Yes it's 256K/64K, however 
it's 2x the cost of the 64K/16K, and about 40% more expensive than 
the LPC2148 512K/40K.  The LPC2148 is the same price as the 
128K/32K, so with that comparison I can get more memory with the 
LPC.  However I don't know why the LPC doesn't offer 64KB (or 72KB 
as their logic goes), as that would be a major plus for them.  40KB 
vs 64KB is a larger difference than 128K vs 512K flash, at least in 
some circumstances.

Ethernet is really of no use to me in my short-term plans, an it's 
fairly easy to add in as an external component later on anyway.
 
> There's an open source downloader for the Philips devices, but 
> nothing like that for Atmel. As I understand it there's no linux
> downloader for SAM-BA, and no Windows command-line downloader.

Good point.  Thanks for mentioning that, however I'd imagine (hope!) 
that there will be an open source one soon.
 
> Philips does not support programming flash over USB at all, Atmel 
> does (via their Windows GUI program).

I didn't realize this either.  How fast does the Philips boot-loader 
download at?  If 115.2 then it's not that big a deal, as even 
downloading 512KB can be done in less than 45 seconds.  Usually 
you'll have much less code than that anyway.  As you mention you can 
always create your own bootloader to run over USB.  I imagine that 
someone will make one and open source it pretty soon anyway.

How useful is the 10-bit DAC?  That's too low for MP3 playback, 
isn't it?

Right now the only major pluses for Atmel is the ability to have 
64KB on-chip RAM, and the fact that all peripherals are DMA'd, 
including UART communications.  Philips has much more flash, 128-bit 
memory access (noticeably faster from what I hear), is cheaper, has 
13 more GPIO lines, has a DAC, has 32-bit timers, and is 5MHz faster.

Considering how all of my microcontroller development over the past 
2 years has been with a whopping 12KB of ram, I'm sure that 32KB is 
enough as long as you are smart with your memory usage.  I don't 
plan on doing huge RS232 transfers (for which the DMA would be 
useful on the SAM7S), especially since there is USB available.  Add 
in the fact that I can add external "slow-speed" SRAM to either 
device, and it looks like the LPC2148 is winning the race.

Although I'd still appreciate any comments that anyone else has to 
make.

Thanks!

One thing I find troublesome about the Atmel AT91SAM7Sxx:

There is no guaranteed external Reset pin.

If URSTEN in RSTC_MR is set to 0, asserting NRST will not generate a 
reset.

Hence, I cannot have a hardware reset button which will guarantee 
recovery from any type of possible catastrophic software crash 
(unless I want to actualy remove power from the chip).


--- In lpc2000@yahoogroups.com, "Eric Engler" <englere.geo@y...> 
wrote:
> This is the best comparison I've seen of these popular families. I 
> didn't see you mention Ethernet but maybe that's not a concern for 
you.
> 
> The AT91SAM7X256 should be out by now and that looks great - you 
might 
> want to look at it.
> 
> One issue that concerns me: there's an open source downloader to 
> program flash on Philips devices, but nothing like that exists for 
the 
> Atmel devices yet. As I understand it (someone correct me if I'm 
> wrong), there's no linux downloader (of any kind) for SAM-BA, and 
> there's no commandline downloader for Windows. 
> 
> Commandline downloaders are convenient to use with various IDEs 
that 
> don't have built-in JTAG support. An open source downloader gives 
us 
> IDE authors a good example of how to integrate support for it into 
> IDEs.
> 
> I didn't check to see if Atmel fully documented the SAM-BA API, but 
it 
> seems like its closed. They also didn't seem to publish the API for 
> their DLL either. Or maybe this stuff is documented somewhere, or 
> maybe it will be soon. Atmel seems like a fairly open company so 
I'm a 

> little confused about this.
> 
> However, it's also fair to point out that Philips does not support 
> programming flash over USB at all (you could roll your own code, of 
> course). but Atmel does (if you can make use of their Windows GUI 
> program).
> 
> Eric