When to use Emulation when to use Hardware,when to use Virtual devices.Re: Software Emulator

[John Carter]

On Sat, 17 Feb 2007, Koen Kooi wrote:

>> If you don't like using an emulator, by all means, don't, but please
>> understand that, whether the desire is rational or not, the rest of us
>> prefer them.

> Amen to that. To clarify: y response was incited by repeated
> statements of "need an emulator to see how openmoko looks like",
> which is simply isn't true.  regards,

As a guy that develops development environments for a living... let
me say there is a lot of middle ground in this argument....

You see, I have found it depends critically on what you are doing with
the device.

If you are writing hardware device drivers, you need the real
hardware. Period. With JTAG's and any tool you can lay your hands on.

If you are porting compilers / toolchains / bootcode / OS's, then
sometimes NOT having real hardware and having a plain CPU emulation is
easier. ie. Fight one issue at a time, get your code working and
debugged on the emulator, then try on real (usually slightly buggy)
hardware.

If you are working at the Application level, it is _way_ _way_ nicer
just to work in a Bog Standard Linux Desktop Native
environment. Everything is _way_ faster, your tools are _way_ better &
smarter (valgrind, gcov, gprof, gdb, compile,link,d/load,run
cycle....)

But.

There is a Gotcha.

You need to be able to talk to and receive stimulus from the real
hardware (or a really good facsimile thereof) ie. The phone stack, the
GPS, the ...)

That can be handled two ways.
   * Completely virtualized.

   * Some back channel communication that has stubs on the desktop
     connecting to stubs on the dev board. (Good for doing the
     development of the lower layers of the comm stack)

The answer is you can get damn far in application development with a
good way of virtually providing the stimuli needed.

In the OpenMoko environment what do you need?

  * The guys doing the real platform development and writing drivers
    for new devices etc. Yup. Need real hardware.

  * The guys doing the OS port and the compiler toolchain, may find a
    CPU emulator of some use. (Real Hardware sucks, it suffers from
    things like bad connections, limited ram, slow connections,
    ummfeatures, ....all problems that stop you working on your part of
    the problem. Let the h/w, boot and device driver guys do their
    thing)

  * The guys doing application development need to realize they aren't
    in "embedded device" Kansas anymore. You _must_ write your code to
    sit atop ordinary Linux. Not wired as directly and shortly to the
    hardware as many embedded system folks are use to. ie. If you need
    the real hardware to get it to run, you are doing it wrong!

  * Once the Application is working, tested and debugged. Then you need
    absolutely vanilla bog standard mass market hardware to do
    integration and functional testing on. (Test like you fly, fly what
    you tested)

John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter at tait.co.nz
New Zealand