FPGA Central

What is different between general micro-controller and FPGA soft
processor?

Speed?
Cost?
Easy to use?
Easy to learn?

I am curiouse if the soft controller will replace the regular
microcontroller?

Xilinx said they implement 32-bit RISC controller with a lot of
benefits. Would that replace ARM?

kathy wrote:
> What is different between general micro-controller and FPGA soft
> processor?
>
> Speed?

On the same process, a soft processor will always be slower, but
soft processors have other benefits :
You can deploy more than one very easily, and can choose the
resource level. The FPGA process tends to be leading edge, so
that reduces the actual speed penalty - but at the cost of
static Icc.
Soft processors can also readily connect to the other logic

> Cost?

On a pure silicon basis, a soft processor will always be more
expensive.
BUT if you already have the FPGA for other tasks, the
_incremental_ cost of a soft processor can be quite low.


> Easy to use?
Improving all the time
A weakness of soft processors, is code memory/boot memory has
to be separate. That's a lot of PCB traces, and much EMC...

A valid alterative would be to use an external Flash Microcontroller,
with a high speed serial data interface to the FPGA, for example.

> Easy to learn?
Reasonably, given that you will be doing the FPGA Logic design
as well.

> I am curiouse if the soft controller will replace the regular
> microcontroller?

Complement is a better description than replace, tho I am
sure the Marketing Depts of the FPGA vendors would claim
otherwise....
It is quite common to see a number of microcontroller and
micro-processor/DSP working together in a single product.

> Xilinx said they implement 32-bit RISC controller with a lot of
> benefits. Would that replace ARM?

Xilinx also offer PowerPC cores. If the Soft processor was
a universal solution, ask yourself why would they bother doing that ?

-jg

"kathy" <[email protected]> wrote in message
news:[email protected] om...
> What is different between general micro-controller and FPGA soft
> processor?
>
Just to add to what Jim says, a big difference is that soft processors don't
go obsolete.
Cheers, Syms.

Another consideration is that soft processors allow customization. It
is relatively easy to add a special purpose hardware DSP function to a
soft micro.

Using off the shelf components requires a new component for a new
function.

[email protected] (kathy) wrote in message news:<[email protected]. com>...
> What is different between general micro-controller and FPGA soft
> processor?
>
> Speed?
> Cost?
> Easy to use?
> Easy to learn?
>
> I am curiouse if the soft controller will replace the regular
> microcontroller?
>
> Xilinx said they implement 32-bit RISC controller with a lot of
> benefits. Would that replace ARM?

The problem with a soft processor is that you are never finished. I am
sitting with various versions of NIOS and their related SDKs. Cost is also
high. A Cyclone with config chip + RAM and Flash will be several times the
cost of a gemeral micro. I have several projects where that kind of cost is
no problem. Another drawback is small to medium quantity manufacturing
requires extra config steps.

Advantages with a soft core are plenty. The speed problem is counteracted by
the capability of hard wired silicon co-processing. Once you learn your tool
set (NIOS in my case) then the rest is easy. Be careful not to replace your
trusty PIC or 8051 with a FPGA. If your 8051 can do the job then use your
8051, end of story. As soon as you have equal trade-off point then look at
FPGAs. I have several access control applications where I need direct
interfacing to passive readers, plenty of serial lines, large storage and
medium speed (20-60 MHz). NIOS on a Cyclone serves me well. I still use
Atmel 8051s on many other parts of my system because of the low cost. FPGAs
can also save you a lot on board space, if your application requires a
certain amount of resources. As soon as your board requires plenty of I/O
(several 8255s), lot of memory (16 to 32 bit), more UARTs and other
peripherals then a FPGA with a soft core will look more attractive. If you
can get away with one or two AVRs, 8051 or PICs then use those chips. If
your board starts looking like an old mini-computer's main CPU board (i.e.
very large) then look at the FPGA. I have several design constraints like
euro card size that I have to comply with.

Smaller is not always cheaper. A 32 bit FPGA core will require 32 data
lines, 20 + address lines and several control lines. This excludes your
other I/O. Also you will require a config PROM (unless you are using a Actel
Flash based FPGA). Your PCB ends up complicated and multilayered. And don't
think of staying double sided and going longer tracks. Your super duper FPGA
has very fast rise times that will play "ring-ring" with long tracks.

Power supplies: Hmm. Big problem. Your common micros usually run of a single
power supply. So you can power the device from a single 5V or 3V3 power
supply. FPGAs are not good at this. Most of the newer devices requires at
least 2 power supplies, namely 3V3 for I/O and some other obscure voltage
for the core (e.g. 1.5V). Try to find a cheap 1.5V regulator. Also do the
math with the drop voltage times the current drawn. Another problem is the
inrush current on SRAM devices (like Altera and Xilinx devices). They can
suck up like 1A of current during startup, and then draw very little
afterwards. This requires using a higher current regulator. Your will end
up with at least one switcher and one linear regulator. Extra cost. FPGAs
are not cheap on power. If your system can afford it then go for it. A FPGA
is not a 10mA max device. Go and check the specs.

So do the trade offs: Cost/ Complexity/ Tools/ PCB layers/Size/
Power/Availability/Copy protection.... the list is long.

Each device fills a market. There is no real threat of FPGAs taking over ARM
CPUs. After you have done your trade-offs you will find the optimal
solution. I chose NIOS because it fills about 50% of my systems's
requirements.


Are soft core CPUs cool? Yes. Do I use them for everything? No!


Victor Schutte

[email protected]

http://www.zertec.co.za


"kathy" <[email protected]> wrote in message
news:[email protected] om...
> What is different between general micro-controller and FPGA soft
> processor?
>
> Speed?
> Cost?
> Easy to use?
> Easy to learn?
>
> I am curiouse if the soft controller will replace the regular
> microcontroller?
>
> Xilinx said they implement 32-bit RISC controller with a lot of
> benefits. Would that replace ARM?