[ts-7000] Re: Baffled by MAX197 A/D converter on TS-7250 - solved

["randomyellowbits" <>]

Thank you, thank you, thank you.  Adding O_SYNC brought the
wait-loop counts down into the low 20's, and the readings are
reasonable.  Problem solved.

The defective open statement I copied from the code sample
in the July, 2009 version of the "Linux for ARM on TS-72XX
User's Guide".  That's the latest version I've come across.
I'll try to alert the appropriate authorities.

--- In  "Charles" <> wrote:
>
> 
> Hi --
> 
> Did you remember to use O_SYNC when you opened /dev/mem?
> 
> regards, .....Charlie
> 
> PS - There is also a MAX197 device driver in the 'files' section of this 
> group; it worked quite well for me with high speed sampling.
> 
> --- In  mike ingle <finndmike62@> wrote:
> >
> > Hi
> > I can't answer your question, but I can say I have seen this topic several 
> > times.  Please search the archives (try  "MAX197"), and I think you will 
> > find your answer.  Google yields 580 results from "TS7250 MAX197".
> > 
> > Best regards, and you will generally find this group to be helpful.
> > 
> > Mike
> > 
> > 
> > On Sep 29, 2011, at 5:40 PM, randomyellowbits wrote:
> > 
> > > I'm trying to understand the MAX197 A/D converter on my TS-7250, but its 
> > > behavior differs wildly from my expectations. I hope someone here can 
> > > tell me what I'm missing.
> > > 
> > > For starters, after writing a control byte to 0x10c00000, I typically 
> > > have to poll 0x10800000 a couple million times before the INT* line 
> > > (0x80) goes low. This doesn't seem consistent with a conversion time on 
> > > the order of 10 microseconds.
> > > 
> > > Secondly, according to my reading of the MAX197 specs, the act of reading 
> > > the result sends INT* high again; but it typically takes a couple million 
> > > passes through the polling loop before it goes high.
> > > 
> > > If I don't wait for INT* to go high before initiating another conversion, 
> > > it will still be low after I write the control byte, which looks as if 
> > > the conversion is completed, but if I optimistically read the result, the 
> > > low-order byte of the result is identical to the control byte I just 
> > > wrote.
> > > 
> > > Being new here, I'm not sure how much code I'm welcome to post, so here 
> > > are the bare essentials:
> > > 
> > > #define MMAP(x) mmap(0,getpagesize(),PROT_READ|PROT_WRITE, 
> > > MAP_SHARED,fd,x);
> > > 
> > > static volatile unsigned char *initiate;
> > > static volatile unsigned short *adresult;
> > > static volatile unsigned char *installed;
> > > static volatile unsigned char *complete;
> > > 
> > > initiate = (unsigned char *) MMAP(0x10c00000);
> > > complete = (unsigned char *) MMAP(0x10800000);
> > > installed = (unsigned char *) MMAP(0x22400000);
> > > adresult = (unsigned short *) initiate;
> > > 
> > > Thanks in advance for informative comments, or even illuminating insults.
> > > 
> > >
> >
>




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