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_posts/2023-07-07-embedded-phy.markdown

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+---
+layout: post
+title:  "Embedded systems from ground up: PHYnal Fantasy"
+date:   2023-07-07 18:47:00 -0300
+categories: hardware embedded
+tags: hardware embedded yocto networking
+---
+
+On my last post about embedded systems and the Orange Pi One Plus, I mentioned that I was having trouble with ethernet. This is all documented on [1] and [2] but I wanted to document this in my blog as well.  
+
+Basically, ethernet doesn't seem to work out of the box on the Orange Pi One Plus and on the upstream u-boot and I want to understand why. 
+
+One thing I found out from the device dts: 
+
+```
+        reg_gmac_3v3: gmac-3v3 {
+                compatible = "regulator-fixed";
+                regulator-name = "vcc-gmac-3v3";
+                regulator-min-microvolt = <3300000>;
+                regulator-max-microvolt = <3300000>;
+                startup-delay-us = <100000>;
+                enable-active-high;
+                gpio = <&pio 3 6 GPIO_ACTIVE_HIGH>; /* PD6 */
+                vin-supply = <&reg_aldo2>;
+        };
+```
+
+This is the definition of the voltage regulator for PHY. I still don't really understand what PHY is, but it is important for making ethernet work. This line: 
+
+```
+gpio = <&pio 3 6 GPIO_ACTIVE_HIGH>; /* PD6 */
+```
+
+is something that made me try a lot of things before reading the datasheet (always read the datasheet!). I saw this GPIO and thought "hey, let me short pin 3 and 6 and it will work". After some tries, it did, but I couldn't replicate, 
+so I believe I just glitched the board. 
+
+The datasheets and all the stuff related to this board is on a Google Drive [3]. Looking at the Allwinner H6 datasheet, I saw that the `GPIO3_6` (or PD6) was not accessible through the header, but it was accessible through u-boot.
+
+I gave it a try, after a few reboots and with this config: 
+
+```
+u-boot config:
+
+CONFIG_SPL_SPI_SUNXI=y
+CONFIG_SUN8I_EMAC=y
+
+tfa config:
+SUNXI_SETUP_REGULATORS=1
+```
+
+I was able to get eth0 (and for some reason it only shows up after a lot of restarts). And then, on the shell:
+
+```
+gpio set pd6
+```
+
+After that, the LED on ethernet started blinking! However, the dhcp command failed... it worked once, I don't know how, but it fails consistently now. 
+
+The Orange Pi One Plus has an interesting schematic that shows exactly this pinout. It's very hard to read and understand, but I'll make sense out of it soon:
+
+![Orange Pi RGMII schematics](/assets/img/opischematics.png)
+
+The EMAC section of the Allwinner H6 datasheet seems to match this pinout
+
+![Allwinner H6 Datasheet](/assets/img/allwinner.png)
+
+From the Realtek RTL8211E datasheet, I could figure out that MII is 100mbps while RGMII is gigabit. Interesting!
+
+![Realtek RTL8211E datasheet](/assets/img/realtek.png)
+
+Okay, so, when we enable the PD6 pin, what are we enabling on RGMII? To try to make sense, I made this spreadsheet:
+
+![PHY pins](/assets/img/phypins.png)
+
+Quite surprising why they use PD6 for voltage regulation. Strange, actually. I don't understand why.
+
+LOL, the quick way to enable eth0 is to do a `mii dump` and let u-boot crash and restart.
+
+I'm quite tired now, I'll leave this link in Chinese here \[4] (ps.: I should definitely continue studying Chinese!) which has some information about the LicheeZero u-boot ethernet. I believe they both have the same processor, so maybe its config
+should have some clue. I need to rest now.
+
+> *_NOTE_* this post is being updated as I figure stuff out.
+
+# References 
+
+\[1] [Ethernet not working on Orange Pi One Plus_](https://github.com/linux-sunxi/meta-sunxi/issues/387)
+
+\[2] [[bug report] sunxi: H6: no ethernet on Orange Pi One Plus](https://lore.kernel.org/u-boot/d0427cea18fad6e36537931962fa5070b084045e.camel@collabora.com/T/#t)
+
+\[3] [Orange Pi One Plus datasheets](https://drive.google.com/drive/folders/1i_jeJRCf0Sr5p62RMo5xodUwTFXELpEi)
+
+\[4] [以太网使用指南](https://licheezero.readthedocs.io/zh/latest/%E9%A9%B1%E5%8A%A8/Ethernet.html#id1)