Serial Port changes with Raspberry Pi 5

Added documentation changes for Serial Port Usage with Raspberry Pi 5, thanks @aGGreSSiv for the research.

Author: domschl

README.md

@@ -18,10 +18,11 @@ Stratum-1 NTP time server with Raspberry Pi, GPS and Chrony:
 While you can use any model of Raspberry Pi to implement a Stratum-1 NTP server with GPS, the best choice
 is Raspberry Pi 4, due to 1Gbit network interface and fast hardware for lowest possible latencies.
 
-  - Using a Raspberry Pi 5 gives two additional advantages:
+  - Using a Raspberry Pi 5 gives two additional advantages, but has changed the configuration of the serial port.
 
     - Support for the inbuilt hardware real time clock (RTC) that comes with the Raspberry Pi 5
     - Support for the PTP protocol, which allows to transmit precision time information via ethernet hardware
+    - When connecting the GPS receiver via serial port, the new default is not to use the RX, TX pins on the 40pin connector, but the new three-pin UART connector. To use the 40-pin connector a special configuration is needed.
 
 Both options are of limited advantage for most settings: the hardware clock is only useful for providing time during the first few seconds after boot (and if both GPS _and_ network are inaccessible), and PTP is a time standard requiring IEEE1588-enabled hardware everywhere and provides no advantages over NTP/chrony in most settings. Both however are documented below (See `chrony` configuration, PTP-chapter).
 
@@ -30,7 +31,7 @@ Both options are of limited advantage for most settings: the hardware clock is o
   * Adafruit GPS hat: [Adafruit ultimate GPS hat](https://www.adafruit.com/product/2324)
   * GPS module with serial output and PPS signal: [Adafruit GPS module](https://www.adafruit.com/product/746)
   * GPS module with USB, SMA connector and PPS: [Keystudio GPS module](https://wiki.keyestudio.com/KS0319_keyestudio_GPS_Module)
-  * Cheap NEO6 modules: [Aliexpress NEO6](https://www.aliexpress.com/item/32800500501.html?spm=a2g0o.productlist.0.0.2eae3298PesRP8&algo_pvid=89486c29-bfb7-414c-a88d-81a9972f8080&algo_expid=89486c29-bfb7-414c-a88d-81a9972f8080-1&btsid=2100bdd516068129046292696e617f&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_)
+  * Cheap NEO6 modules: [Aliexpress NEO6](https://www.aliexpress.com/w/wholesale-neo6.html))
 
 <img src="https://github.com/domschl/RaspberryNtpServer/blob/main/images/antenna.jpg" align="right" width="200" height="200" />
 
@@ -73,6 +74,7 @@ Serial connection:
 * All Pi Hats use serial connections.
 * Raspberry serial console needs to be disabled
 * Sometimes, bluetooth needs to be disabled.
+* Raspberry Pi 5 changed the default serial connection to the 3-pin UART connector by default.
 
 ### Recommended setup
 
@@ -90,6 +92,20 @@ _Typical wiring between GPS module and Raspberry Pi connector._
 
 > **Note:** If your GPS module is connected via USB, you only need to connect the PPS connector on the GPS module to GPIO 4 on the Raspberry. Power (Vin), Gnd and Tx/Rx are handled via USB.
 
+> **Note:** The Raspberry Pi 5 has a new connector for the serial port that is used by default instead of the Pins RX, TX on the diagram:
+
+#### Raspberry PI 5 serial connection changes
+
+- Either use _new the three-pin UART connector_, which is used by default for serial communication,
+- or reconfigure the serial ports by editing `/boot/firmware/config.txt` and adding the lines:
+
+```
+dtparam=uart0
+dtparam=uart0_console
+```
+
+Documentation for those options is currently in a disarray for Raspberry Pi 5, so some research might be required. See discussion in [#6](https://github.com/domschl/RaspberryNtpServer/issues/6). Also this [video on Raspberry Pi 5 Serial Port](https://www.youtube.com/watch?v=27p4XHE3iyw) usage might be helpful.
+
 ### Test
 
 **Before you continue with software:** At this point, the GPS module should be connected to the Raspberry Pi and the active antenna. Power up the Raspberry Pi, and check that the GPS module receives the GPS signal (the antenna must have unhindered access to the open sky, it does *not* work indoors!).
@@ -602,6 +618,7 @@ Optionally, you can use [this sub-project to a status display to the Raspberry P
 
 ## History
 
+- 2024-04-30: Changes to Raspberry Pi 5 serial Port configuration, see [6](https://github.com/domschl/RaspberryNtpServer/issues/6), thanks @aGGreSSiv for figuring out the issue!
 - 2024-03-06: Update: location of `/boot/config.txt` has changed to `/boot/firmware/config.txt`. Thanks to @Nebulosa-Cat for the information!
 - 2023-12-21: Cleanup for the display software, display current stratum level (thanks @Lefuneste83, see [#7](https://github.com/domschl/RaspberryNtpServer/issues/7)), implemented logging.
 - 2023-12-20: Raspberry 5 and suport for RTC and PTP precision time protocol how-tos.