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--- pixo_replacement [2023/03/27 03:35] – millerjs
+++ pixo_replacement [2024/11/14 02:30] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ====== Raspberry Pi XO Replacement ======
+Context:
   * https://raspberrypi.stackexchange.com/questions/74482/switch-out-the-x1-oscillator-on-a-rpi-2-3/109074#109074
@@ Line 26: / Line 27: @@
   * 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 ====
-  * [[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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