Sad Story

[Karthik Kumar]

Okay, Al. That's one of the most sensible replies on this thread; I hear
ya. I'll dig deeper into this.

Al Johnson wrote:
> On Monday 15 December 2008, Karthik Kumar wrote:
>   
>> On Mon, Dec 15, 2008 at 5:35 AM, Stefan Monnier
>>
>> <monnier at iro.umontreal.ca> wrote:
>>     
>>>>>> There are still hardware problems that exist with almost every
>>>>>> freerunner out there (GPS signal levels, for one).  I would like to
>>>>>> see them fixed by Openmoko, Inc.
>>>>>>             
>>>> The kernel fix for GPS is a mere quirk. Ideally it should get fixed in
>>>> hardware.
>>>>         
>>> Huh?  The kernel fix seems to work OK for those people who have old
>>> FRs.  Newer FRs have a hardware fix.  E.g. my FR doesn't need any
>>> kernel workaround.  No need to wait for GTA03 to get a hardware fix.
>>>       
>> So, this kernel fix is a feature, according to Al Johnson? Then why do
>> they need a hardware fix?
>>     
>
> They don't. Neither of my Freerunners has the hardware fix, and the GPS works 
> just fine with any kernel that includes the fix.
>
>   
>> Unless I am missing something, this software  
>> fix seems to be a lie. Or the hardware fix seems to be bogus anyway.
>>     
>
> You are missing something, so I will try to explain. The 'hardware fix' is a 
> small capacitor from the SD clock line to ground, and was a quick response to 
> the problem when the SD was discovered to be interfering with the GPS. This 
> slows the transition between the digital high and low states, reducing the 
> level of interference generated. Reducing the drive strength does the same 
> thing, but through a slightly different mechanism, and doesn't require a 
> soldering iron to make the change. Note that the hardware fix only reduces 
> interference from the clock line. The kernel fix reduces interference from 
> the other signal lines too.
>
> To understand the issues more fully I suggest you read up on the analogue 
> properties of digital electronics, particularly in regard to the speed of 
> transitions and their effect on EMI.
>
>   
>> I have one of the earlier freerunners released, so I'm sure Openmoko
>> owes an explanation.
>>     
>
> Both hardware and software fixes were discussed extensively on the lists, and 
> are in the list archive. 
>
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