[Gmecm] On the fly tuning

[Darren Freed]

Sorry if this is a repost - I haven't seen it come through yet, thought I'd
try again.

>
On the 96/97 v6 PCMs, the SCI is unlocked and enabled to allow access to the
PCM.  It's functionality is very limited, although it does support a P4
style Mode 5/6 (download and execute).  The OBD-II serial flash paper on the
gmecm webpage is based on that capability.  In stock form, the SCI is used
to communicate with the ABS and digital dash etc.  With newer pcms, that is
handled by the J1850 bus, so the SCI capability is dropped completely
(although oddly enough the code is still there - just never called).  I
expanded the SCI capability to allow P4 style Modes 1/2/5/6/8/9 and even
made up a few of my own, for example writing to the RAM expansion.  The
initial changes to code/reflashing had to be done with Steve Ravet's BDM
utilities, but now I only use the SCI to reprogram the flash (except for
rescuing dead boxes).  I'm not sure how many PCMs would support this type of
thing, which is why we really need to jump on Steve's J1850 VPW interface
and develop software for it - with it, any PCM could be configured for this
(with or without code changes) although to implement RAM expansion (which
could also be read/written over the J1850 bus, with code changes), an edge
connector is handy (not all of them have it - particularly the newer ones).

The RAM is implemented using 2 unused chip select pins and setting up their
respective configuration registers in the SIM.  As far as the PCM is
concerned it is no different than reading/writing one of the peripheral
chips.  It is set up nearly identical to the efi332 project in terms of
addressing.

I really need to find some time to put this altogether into a nice little
package (along with all my P4 stuff) and put it up on the new Wiki!!  I
really need another body!  :-)

Darren


On 7/4/06, Craig Moates <craig at moates.net> wrote:
>
> Darren,
>
> OK, so the code on the external flash has been modified to enable the SCI
> handler for direct access?
>
> So all you need is a serial comm at the SCI port pins of the CPU/edge
> connector to carry this out from the PC/external perspective.
>
> What does the 'stock' code provide for with respect to SCI handling, and
> how did you expand it? I mean, in stock form, what can be
> done with the SCI port? Can you do small RAM dumps, like some of the old
> Mode1/Mode2 ALDL stuff? What are the protocols for talking
> with the CPU via the SCI port. I'm asking because I think that your SCI
> stuff could be very useful to several folks.
>
> Also, for your expansion RAM, did you keep the address and data lines
> common with those of the external flash chip? So that you just
> select whether you're in RAM or ROM with a CE1/CE2 pairing?
>
> Best regards,
> Craig Moates
>
>
> ----- Original Message -----
> From: "Darren Freed" <darrenfreed at gmail.com>
> To: <gmecm at diy-efi.org>
> Sent: Tuesday, July 04, 2006 2:16 PM
> Subject: Re: RE: [Gmecm] On the fly tuning
>
>
> > The amount of RAM on the CPU itself is quite small, not practical for
> the
> > kinds of things the diy-efi community wants to do (I reckon,
> anyway).  So
> > yeah, I've modified the 'stock' code to point to my external RAM for
> table
> > lookups.  The actual 'OS' still runs as usual from the flashrom.  I've
> > expanded the PCMs SCI handler to include a mode that will accept values
> over
> > the SCI and stores them in my additional RAM (ie table lookup values),
> > enabling on the fly modification of tables.
> >
> > Or am I misunderstanding what you mean by "anything that is stored on
> the
> > CPU itself?"
> >
> > Darren
> >
> >
>
>