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pixo_replacement [2023/03/10 17:53] – [Test Cases] millerjspixo_replacement [2024/11/14 02:30] (current) – external edit 127.0.0.1
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 ====== Raspberry Pi XO Replacement ====== ====== Raspberry Pi XO Replacement ======
 +Context:
   * https://raspberrypi.stackexchange.com/questions/74482/switch-out-the-x1-oscillator-on-a-rpi-2-3/109074#109074   * https://raspberrypi.stackexchange.com/questions/74482/switch-out-the-x1-oscillator-on-a-rpi-2-3/109074#109074
 +
 +==== Success! ====
 +Made an initial attempt on the evening of 2023-03-26 on a Pi 2 B. Drop in replacement is working surprisingly well right off. Have not performed any longitudinal testing yet, but initial tracking numbers are positive.
 +
 +^  Pi 2 B with replaced XO           ^  Pi 2 B with stock XO                ^
 +| {{::pib-newxo-tracking.png?400|}}  | {{::pib-stockxo-tracking.png?400|}}  |
  
 ==== Notable Test Points ==== ==== Notable Test Points ====
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   * http://www.farnell.com/datasheets/2860337.pdf   * http://www.farnell.com/datasheets/2860337.pdf
 +
 +As far as I can tell, the Pi 2B through 3B+ all use this part, as well as a number of the A models. The Pi 4B uses two AEL crystals, one at 25MHz, the other at 54MHz. I have not yet experimented with replacing these parts. 
  
 ==== New TCXO ==== ==== New TCXO ====
-  * [[https://media.digikey.com/pdf/Data%20Sheets/IQD%20Frequency%20PDFs/LFTCXO079058.pdf|IQXT-205-3-18]]+  * [[https://www.digikey.com/en/products/detail/iqd-frequency-products/LFTVXO079052/9739101|IQXT-205-3-18]] or 
 +  * [[https://www.digikey.com/en/products/detail/taitien/TXETBLSANF-19-200000/6127626|TXETBLSANF-19.200000]]
  
-==== Test Cases ==== 
-Before I do this swap, I need to get a benchmark of (at least) two identical Pis so I have a baseline of their performance in stock configuration. These systems need to be as identical as possible, both in terms of software load out as well as their physical deployment.  
  
-=== Software === +====== Quantifying Results ====== 
-  * OS - Alpine Linux 3.17 +There are a number of different methods for quantifying the results of this sort of modification. A few that I am exploring will be detailed below. 
-  * Timekeeping/measurement - chrony+==== chrony tracking ===== 
 +(Graphs coming eventually) 
 +==== Python Frequency Generator ==== 
 +  * [[https://sourceforge.net/p/raspberry-gpio-python/wiki/PWM/]] 
 +  * [[https://gist.github.com/boseji/7296415]]
  
-Configured to be as light and slim as possible.+<code python sigGen.py> 
 +#!/usr/bin/python
  
-=== Physical === +import RPi.GPIO as GPIO 
-This will be an isolated test, no +from time import sleep
-== Power == +
-Meanwell 5v PSU powering both Pis - "back feeding" through the 5v pin on the 40p header. AC PSU connected to a UPS to protect against brownouts or extended outages.+
  
-== Environmental == +GPIO.setmode(GPIO.BCM) 
-Both Pis enclosed in a single styrofoam enclosure, as close to each other as reasonable. Placed in a location that is as temperature stable as possible (no direct sunlight, no temp swings from HVAC adjacency, etc.)+GPIO.setup(10,GPIO.OUT) 
 +p=GPIO.PWM(10,1140) 
 +p.start(20) 
 +sleep(3600) 
 +p.stop() 
 +GPIO.cleanup() 
 +exit() 
 +</code> 
 + 
 +==== WiringPi GPIO_CLOCK ==== 
 +The WiringPi toolset has a function to use the SoC's PLLs to generate a precise clock using the GPIO_CLOCK function. This can be initiated easily from the linux userspace by first setting the pin mode, then the output frequency. Only WiringPi Pin 7 (GPIO 4) supports this mode. 
 + 
 +<code> 
 +gpio mode 7 clock 
 +gpio clock 7 1000000 # frequency in Hz 
 +</code>
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