Hi everyone,

I am planning to learn Java.

Can I access HW registers in Java? Or can I call C function from Java
program?

Thanks.

On Mon, 13 Aug 2007 22:07:16 -0700, dick wrote:

> Hi everyone,
> 
> I am planning to learn Java.
> 
> Can I access HW registers in Java? Or can I call C function from Java
> program?
> 
> Thanks.

Even though I don't know much about Java, I know these tidbits:  

No, you cannot directly access hardware from Java.  I would be surprised
to find a serious Java for embedded use that did not include library
functions to do so, however.

Java itself doesn't provide a means to call C functions, but most Java run
time environments provide a means to call external code.  Of course, if
you're calling external code then you have to maintain code bases in C
_and_ Java...

-- 
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:
> On Mon, 13 Aug 2007 22:07:16 -0700, dick wrote:
>
> > Hi everyone,
> >
> > I am planning to learn Java.
> >
> > Can I access HW registers in Java? Or can I call C function from Java
> > program?
> >
> > Thanks.
>
> Even though I don't know much about Java, I know these tidbits:
>
> No, you cannot directly access hardware from Java.  I would be surprised
> to find a serious Java for embedded use that did not include library
> functions to do so, however.
>
> Java itself doesn't provide a means to call C functions, but most Java run
> time environments provide a means to call external code.  Of course, if
> you're calling external code then you have to maintain code bases in C
> _and_ Java...
>
> --
> Tim Wescott
> Control systems and communications consulting
> http://www.wescottdesign.com
>
> Need to learn how to apply control theory in your embedded system?
> "Applied Control Theory for Embedded Systems" by Tim Wescott
> Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html






If I design a HW platform, how can I run Java in this bare machine.

dick <d...@hotmail.com> writes:
[...]
> If I design a HW platform, how can I run Java in this bare machine.

Your first step should be to find a newsgroup with "java" in its name.

-- 
Keith Thompson (The_Other_Keith) k...@mib.org  <http://www.ghoti.net/~kst>;
San Diego Supercomputer Center             <*>  <http://users.sdsc.edu/~kst>;
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

On Aug 14, 9:26 am, dick <dick_12345...@hotmail.com> wrote:
> Tim Wescott wrote:
> > On Mon, 13 Aug 2007 22:07:16 -0700, dick wrote:
>
> > > Hi everyone,
>
> > > I am planning to learn Java.
>
> > > Can I access HW registers in Java? Or can I call C function from Java
> > > program?
>
> > > Thanks.
>
> > Even though I don't know much about Java, I know these tidbits:
>
> > No, you cannot directly access hardware from Java.  I would be surprised
> > to find a serious Java for embedded use that did not include library
> > functions to do so, however.
>
> > Java itself doesn't provide a means to call C functions, but most Java run
> > time environments provide a means to call external code.  Of course, if
> > you're calling external code then you have to maintain code bases in C
> > _and_ Java...
>
> > --
> > Tim Wescott
> > Control systems and communications consulting
> >http://www.wescottdesign.com
>
> > Need to learn how to apply control theory in your embedded system?
> > "Applied Control Theory for Embedded Systems" by Tim Wescott
> > Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html
>
> If I design a HW platform, how can I run Java in this bare machine.- Hide quoted text -
As per my basic understanding, for your hardware platform you need to
Develop or Port Java Run Time Environment <JVM , regret i am not java
guru and This is not Java-news group, regret if you think replying to
OT>

-Raxit
>
> - Show quoted text -

On Mon, 13 Aug 2007 22:26:54 -0700, dick wrote:

> Tim Wescott wrote:
>> On Mon, 13 Aug 2007 22:07:16 -0700, dick wrote:
>>
>> > Hi everyone,
>> >
>> > I am planning to learn Java.
>> >
>> > Can I access HW registers in Java? Or can I call C function from Java
>> > program?
>> >
>> > Thanks.
>>
>> Even though I don't know much about Java, I know these tidbits:
>>
>> No, you cannot directly access hardware from Java.  I would be surprised
>> to find a serious Java for embedded use that did not include library
>> functions to do so, however.
>>
>> Java itself doesn't provide a means to call C functions, but most Java run
>> time environments provide a means to call external code.  Of course, if
>> you're calling external code then you have to maintain code bases in C
>> _and_ Java...
>>
>> --
>> Tim Wescott
>> Control systems and communications consulting
>> http://www.wescottdesign.com
>>
>> Need to learn how to apply control theory in your embedded system?
>> "Applied Control Theory for Embedded Systems" by Tim Wescott
>> Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
> 
> 
> 
> 
> 
> 
> If I design a HW platform, how can I run Java in this bare machine.

You need a Java run-time environment to run Java, at which point the
machine would no longer (by my definition) be "bare".

-- 
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

On Aug 13, 10:26 pm, dick <dick_12345...@hotmail.com> wrote:
>
> If I design a HW platform, how can I run Java in this bare machine

A typical embedded system will not have the CPU
power or memory to interpret the bytecode at
runtime, so that leaves two options:

1.  Use a compiler that generates native machine
    code.  See http://gcc.gnu.org/java/

2.  Use a uC that includes hardware support for
    Java bytecodes.  There are several inexpensive
    (less than $10) microcontrollers based on the
    ARM926EJ-S core, including Atmel's AT91SAM9260
    and NXP's LPC3180.

My opinion is that Java is a poor language
choice for most embedded system projects.  But
you can come to you own conclusion about that.

[comp.lang.c removed from newsgroups]

On Mon, 13 Aug 2007 22:07:16 -0700, dick wrote:

> Hi everyone,
> 
> I am planning to learn Java.

	So you can compile programs once in one platform, and run them 
nowhere?

> Can I access HW registers in Java? 

	I bet you can't.

> Or can I call C function from Java program?

	Yes - using JNI. The catch is that the overhead introduce by this 
is such that in most cases the resulting code is almost as slow as an all 
Java code.

Ivar Rosquist wrote:

> On Mon, 13 Aug 2007 22:07:16 -0700, dick wrote:
> 
>> Hi everyone,
>> 
>> I am planning to learn Java.
> 
>       So you can compile programs once in one platform, and run them 
> nowhere?

Don't be (a) silly (b) atopical.
 
>> Can I access HW registers in Java? 
> 
>       I bet you can't.

You can't in C, either.

>> Or can I call C function from Java program?
> 
>       Yes - using JNI. The catch is that the overhead introduce by this 
> is such that in most cases the resulting code is almost as slow as an all 
> Java code.

That is, of course, going to depend on how much work the C code does;
"most cases" is sheer handwaving. 

-- 
Chris "(render unto \X that which is X's)(C | Java)" Dollin

Hewlett-Packard Limited registered office:                Cain Road, Bracknell,
registered no: 690597 England                                    Berks RG12 1HN

[X-post lacked a F'up2; reduced to one group]

dick wrote:

> I am planning to learn Java.

Why, given you clearly don't know if it's going to do you any good?

> Can I access HW registers in Java? Or can I call C function from Java
> program?

If you must ask, that strongly implies it's a bad idea for you to learn 
Java at this point.  You have to analyze what it means to use Java 
instead of C first.