Soft CPU vs Hard CPU's

Hai all,
          I heard that the SOFT CPU's have wide range of benefits than
the HARD CPU's. if so, then  why still HARD CPU's are preferred.

plz let me know the answer.

regards, 
kishore

Hi (hai means "shark" in my native language)

1 your question doesnt have an answer.
2 and your assumptions are not correct.
3 and if you keep using an identy like "teen" what hardly is your name and
wording in style 'Hai', 'plz' then you hardly will get answers to anything
you ask. If you dont understand what I mean then it would be of benefit for
you to go back to school and learn there something.
4 if you do not get upset to what I said above and do some homework then you
will be able to correct your wrong assumptions and answer your question
yourself.

antti


"teen" <nkishorebabu123@yahoo.com> schrieb im Newsbeitrag
news:1113544130.628433.67240@o13g2000cwo.googlegroups.com...
> Hai all,
>           I heard that the SOFT CPU's have wide range of benefits than
> the HARD CPU's. if so, then  why still HARD CPU's are preferred.
>
> plz let me know the answer.
>
> regards,
> kishore
>

On Thu, 14 Apr 2005 22:48:50 -0700, teen wrote:

> Hai all,
>           I heard that the SOFT CPU's have wide range of benefits than
> the HARD CPU's. if so, then  why still HARD CPU's are preferred.
> 
> plz let me know the answer.
> 
> regards, 
> kishore

You heard wrong. A hard CPU is faster and cheaper then a soft CPU. By
cheaper I mean they take much less die area then an equivalent soft CPU.
The downside of the hard CPUs is that they are only available in high end
FPGAs like the Virtex2P and Virtex4. The cheaper FPGAs like the Spartan3
don't have embedded CPUs. If you needed a processor in a Spartan3 you
would have to use a soft CPU, however you want to use one that was much
simpler then the PPC in the Virtex2Ps and 4s. If you implemented a full
PPC you would use so many slices that you would negate the cost advantage
of the Spartan3.

Cost!!!!

That is the main reason why Hard CPU's are still used. They are
cheaper.... a Phillips Arm 7 32 bit CPU is about $3.50 in quantity. An
FPGA with a similar size softcpu like a Microblaze is about $10.

Soft CPU's are used for performance. They take advantage of the FPGA's
logic and use parallelizm to speed up operatiations (ie multipuly two
32 bit numbers in a single clk cycle). A hard CPU would take 4 or more
clk cycles to multiply two 32bit numbers.

So SoftCPU's used with FPGA logic can have a higher performance than an
equivelent hardCPU.

So it totally depends on your application to whether a soft or hard CPU
is for you.

Eric

SoftCPUs also can have custom peripherals (ie 5 x UARTs, 6 x SPI bues,
20 x I2C bues).

With a Hard CPU your stuck with what the manufacturer gives you.

Personally SoftCPU's are more fun.... custom home brewed CPU's are
exciting!!!

Writing a VHDL model of a CPU is the closest to designing my own CPU
I'll ever get. There is something exciting about that!!!!

Eric

> Writing a VHDL model of a CPU is the closest to designing my own CPU
> I'll ever get. There is something exciting about that!!!!

Er, that is designing a CPU! Probably the large majority of commerical
CPUs are synthesizable, or contain a lot of synthesizable code.

Cheers,
Jon

Antti Lukats wrote:
> Hi (hai means "shark" in my native language)
> 
> 1 your question doesnt have an answer.
> 2 and your assumptions are not correct.
> 3 and if you keep using an identy like "teen" what hardly is your name and
> wording in style 'Hai', 'plz' then you hardly will get answers to anything
> you ask. If you dont understand what I mean then it would be of benefit for
> you to go back to school and learn there something.
> 4 if you do not get upset to what I said above and do some homework then you
> will be able to correct your wrong assumptions and answer your question
> yourself.
> 

Hey Antti,

Don't beat about the bush, man - tell him what you think, straight up! 
This softly-softly approach never works [grin]

[Not to say that I don't agree with your points on the language though :-]

Simon.

> "teen" <nkishorebabu123@yahoo.com> schrieb im Newsbeitrag
> news:1113544130.628433.67240@o13g2000cwo.googlegroups.com...
> 
>>Hai all,
>>          I heard that the SOFT CPU's have wide range of benefits than
>>the HARD CPU's. if so, then  why still HARD CPU's are preferred.
>>
>>plz let me know the answer.
>>
>>regards,
>>kishore
>>
> 
> 
> 

Eric wrote:
> Cost!!!!
> 
> That is the main reason why Hard CPU's are still used. They are
> cheaper.... a Phillips Arm 7 32 bit CPU is about $3.50 in quantity. An
> FPGA with a similar size softcpu like a Microblaze is about $10.
> 
> Soft CPU's are used for performance. They take advantage of the FPGA's
> logic and use parallelizm to speed up operatiations (ie multipuly two
> 32 bit numbers in a single clk cycle). A hard CPU would take 4 or more
> clk cycles to multiply two 32bit numbers.
> 
> So SoftCPU's used with FPGA logic can have a higher performance than an
> equivelent hardCPU.

True enough, but it seems to me an external (or on-chip) hard CPU 
loosely coupled with a "coprocessor" built of FPGA fabric gives you the 
best of both worlds for performance/cost and also minimizes power and 
you don't need lots of address pins going into the FPGA.

Jeff

Spartan 3E should help with this.  The smallest Spartan 3E starts at 
under $2 in quantity (and fits a small MicroBlaze system) for an 
effective MicroBlaze cost of $.48 [1].  You may need a larger device to 
get everything you want, but I did want to point out that the $10 is a 
little high if one is going primarily for cost.  It is not fair to 
compare the entire cost of the FPGA to just a hard processor and then 
use the rest of the FPGA for other stuff.  In this case the FPGA is 
doing a lot more than the hard processor.

As far as the benefits of a soft processor.  MicroBlaze is highly 
configurable.  You can turn on the features you need: instruction cache, 
data cache, FSL, XCL, FPU.  See

http://www.xilinx.com/ise/embedded/mb_ref_guide.pdf

for more information on MicroBlaze v4.00.a.

The other huge advantage of soft processors is the FPGA architecture 
itself.  EDK has an FSL wizard to allow easy creation of accelerators. 
With careful acceleration of one's application, one can obtain 
performance that no hard processor can touch.

EDK also includes a lot of other IP allowing one to build a System On a 
Chip (SoC) out of the box.  It is a great deal for the price.

Personally, I also find debugging on an FPGA a lot easier.  One can 
simulate the EDK system and get a ton of information.  I find ChipScope 
a lot more convenient than a logic analyzer and one can dig a lot 
deeper.  Tracking down a bus issue on a hard processor can be a pain. On 
both sides there are lots of good tools if you want to spend the money, 
but I think the costs may be more reasonable on the FPGA side.

If you have the need, Xilinx will sell the MicroBlaze source code for 
you to customize as you see fit.  Try doing that at a reasonable price 
on a hard processor.

I am not in marketing or sales, but I have no problem listing some of 
the advantages of soft processors.

This post is my own opinion, and not an official Xilinx post.  Reverse 
domain and remove the NOSPAM from e-mail address to respond by e-mail.

[1] Xilinx. Xilinx Shatters Price/Density Barrier For Low Cost FPGAs 
With New Spartan-3E Family Starting At Less Than $2.00. 
http://www.xilinx.com/prs_rls/silicon_spart/0531s3e.htm

Eric wrote:

> Cost!!!!
> 
> That is the main reason why Hard CPU's are still used. They are
> cheaper.... a Phillips Arm 7 32 bit CPU is about $3.50 in quantity. An
> FPGA with a similar size softcpu like a Microblaze is about $10.
> 
> Soft CPU's are used for performance. They take advantage of the FPGA's
> logic and use parallelizm to speed up operatiations (ie multipuly two
> 32 bit numbers in a single clk cycle). A hard CPU would take 4 or more
> clk cycles to multiply two 32bit numbers.
> 
> So SoftCPU's used with FPGA logic can have a higher performance than an
> equivelent hardCPU.
> 
> So it totally depends on your application to whether a soft or hard CPU
> is for you.
> 
> Eric

"Benjamin J. Stassart" <benjamin.stassart@MxAnPiSlOiNx.com> wrote in message news:<426457E4.3070600@MxAnPiSlOiNx.com>...
> Spartan 3E should help with this.  The smallest Spartan 3E starts at 
> under $2 in quantity 

"*500K unit volume, second half 2006" !!!

plus you have to factor in the cost of:

 - the configuration prom 
 - extra regulators that you wouldn't need with most micros
 - analog peripherals
 - possibly an oscillator
 - possibly some external RAM

It's not quite a simple as multiple cost-per-LUT by the number of LUTs used.

Cheers,
Jon