[time-nuts] teensy as time capture device

Jim Lux jimlux at earthlink.net
Thu Sep 24 18:55:57 UTC 2015


On 9/24/15 7:13 AM, cfo wrote:
> On Thu, 24 Sep 2015 05:30:35 -0700, Jim Lux wrote:
>
>
>>
>> What would be interesting is if there's a pin on the Arduino/Teensy that
>> you could feed a high quality oscillator to, and then do counting with
>> that.  The K20 microcontroller has a mindbendingly large number of
>> features and alternate pin functions.
>
> As i see it, from the DS. , it seems like there are 2 options.
>
> External Oscillator (the system clock clock) ,
> or External Timer clock (limited to system clock/4)
>
> Electr. specs
> https://www.pjrc.com/teensy/K20P64M72SF1.pdf
>
> Family Ref
> https://www.pjrc.com/teensy/K20P64M72SF1RM.pdf
>
>
> Seems like the EXTAL pin (main oscillator) accepts an Oscillator signal
> (max VDD + 0.3v) (Electr specs pg.10)
>
> Ext Osc Connection (Family ref. pg. 526)
>
> Also see PLL jitter (Electr specs pg.27 table 14)
>
>
> There is a possibility to clock the FlexTimerModule by an external clock
> (FTM_CLKIN/EXCLK - Max freq is Mainclock/4) ,
> see (Family Ref. pg. 113, 214 & 774)
>
>
> If using EXTAL and USB , you want to make sure that the USB part still
> gets it's 48Mhz (via the PLL mul/div).
> Maybe divide 10Mhz (XTAL) by 2 , and mul by 48, in the PLL.

I would think that the FTM_CLKIN would be the way to go.. keep the core 
running at 48 and run 10 MHz in as EXCLK (since it's less than Mainclock/4)

Not sure I'd want to fool with the PLL programming: that's something 
where there might be other stuff that makes assumptions about how it's 
configured.


Now I have to look if the right pins come out to something I can see.
This is the MK20DX256VLH7 configuration.
Only FTM1 (0,1) and FTM2 (0,1) are configured I think.
"There are two external FTM_CLKINx pins that can be selected by any FTM 
module via the SOPT4 register in the SIM module."

Looks like pin 32 and 33 on the chip




Tnx
Jim



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