This thread is intended on collect the information about Android 9 (Pie) over the Android units that features:

• PX5 Platform Core Board
• MTCD/MTCE MCU Type

The information below is a copy of the same thread for Android 6 by @aarick and my own thread for Android 8

• Post 2: Firmware
• Post 3: Tips, Tricks and Fixes - Rooting instruction here
• Post 4: Bugs/Issues
• Post 5: Useful apps
• Post 6: Useful links

For those not familiar with the PX5 Head unit, the specs are below:
OS: Android 8.0 Oreo
CPU: Rockchip PX5 A53 Octa-Core
RAM: 2GB or 4GB DDR3
ROM: 32GB
Audio output: 4*45W
Features:
Built-in Radio Tuner (RDS Enabled) (18 FM and 12 AM stations Preset)
Built-in USB & SD Slot
Region Free DVD Player
Screen Mirroring
Steering wheel controls (SWC) and Canbus interface
Optional compatible accessories:
DAB+ USB Tuner
TPMS
4G/3G Dongle
OBD2 Module
Camera
DVR
External Mic

The head unit comprises of two parts:
a MicroController Unit(MCU) board, which controls physical buttons and A/V inputs/outputs to/from the headunit. This board interacts with Android OS.
ANDROID part. The main Operating System.
Both MCU and Android ROM interact together to achieve the functionality of the head unit.

MCU
MCU type discussed here is MTCD or MTCE (if your unit has not MTCD/MTCE type MCU this thread is not for your unit)
MTCE is a software upgrade for MTCD, so they are identical in terms of hardware

Manufacturers.
The Manufacturer is identified by the XXX when consulting the MCU information under "device information" [MTCE_XXX_Version]. Take into accout that you should always refer the MANUFACTURER name (not the seller) on the forums for help/assistance. Giving the name for the Seller does not give any information but confusion.

e.g: MTCD_HA_1.93_1 (MTCD Unit with MCU for HotAudio under 1.93_1 version)
e.g: MTCE_GS_2.75 (MTCE Unit with MCU for GESHI manufacturer under 2.75 version)

Known manufacturers for MTCD/E PX5 are:
______________ _____________

1. GS = GE_SHI (ShenZhen GESHI Electronics And Technology CO.,LTD. Brands: KA JUN DA. Website: http://www.szgeshi.com )
2. KD = KU_DUO (Shenzhen Kuduo Electronic Technology Co. Ltd.)
3. HA = (Guangzhou Huge Circle Electronic Technology Co., Ltd. Brands: HOTAUDIO/DASAITA. webSite: http://www.hot-audio.com)
4. JY = JIE_YOU (Shenzhen Jieyou Electronic. Brands: JIE YOU J)
5. LM = LEI_MA (Lei Electronics Inc)
6. MX = MAI_XIN (Shenzhen Mai Xin Da Technology Co. Ltd)
7. ZH = ZHI_HANG (Guangzhou Zhihang Electronics Technology CO., LTD. Brands: WINCA/ROADNAV/STQ) http://www.roadnav.com.cn)
8. HZC = HANG_ZHI_CHEN (Same as ZH??)
9. HXD = HE_XIN_DA
10. KGL = KAI_GE_LE (Shenzhen Kaigele Electronics Co., Ltd Brands: HUIFEI. Website: http://www.kaigele.com/enus/)
11. KLD = KE_LAI_DE
12. KSP = KA_SI_PU (Kasi Pu Technology Co., Ltd. Shenzhen)
13. XRC = XIN_RUI_CHANG (Xinrui Electronic Technology Co. Ltd)
14. HLA = (Shenzhen Hualingan Electronic Co. Ltd. Brands:HUALINGAN. Website: http://www.dvdplayer.com.cn/)

(this list will be updated according to users report new manufacturers)

Some information I found on the CPU:
Rockchip PX5 Press Release

Warning for owners of Android 9 PX5 head units.

If you have a firmware version that is newer than end of May or beginning of June, then you cannot install an older version.
This is a new limitation.
If you still try to install an older version, you will get a bootloop.

The following possibilities are available:
When you get a bootloop, you can enter the recovery and install the
latest version. Then the system will work again.

Another possibility would be to install the Android 9 Recovery via the GPS MicroSD slot. From here you can go back to any Android 9 version.

For users without MicroSD slots it is particularly annoying.
With the ModInstaller Pro you can first install the Android 8 Recovery again and then an Android 8 Rom. Then you can update to any Android 9 version.
Look in my signature.

Firmware

Current PX5 Android 9 firmware development:
Stock
Custom
No custom firmwares have been released yet
Installation:
When upgrading from already Android 9:

1. Just copy the update.zip extracted from the downloaded OTA firmware downloaded into a root folder of a USB storage.
2. Upgrade system from Recovery or just update for the specific menu in settings

When upgrading from Android 6 or Android 8 (instructions taken from Hal9K thread)
a) If you have a sdcard slot:

1. Download Hal9k_Mod_3.x_upgrade_to_Android_9.0.rar
2. Uncompress it on PC
3. insert a recently FAT32 formatted micro SDcard into PC (by means of USB adaptor) --> It is recommended 8Gb or lower capacity for this purpose (max working 16Gb)
4. execute the SD_Firmware_Tool.exe file
5. Select the Drive which the sdcard is detected by your PC as target
6. Check that only the option "Update Firmware" is marked
7. on Firmware select the provided file: bootcard.img on Parent folder
8. Press "Create"
9. Wait for the bootable SDcard is created
10. Go to the Sdcard and replace the file sdupdate.img with the one provided on Parent Folder
    in the HeadUnit:
11. insert micro sdcard on the slot marked as GPS/sdcard
12. reboot Unit -> Settings > Factory Settings: Password--> hctreboot
13. the recovery will be automatically upgraded and loaded into display
14. Use the USB with the upate.zip file in root folder and plug into the USB port
15. select on recovery: Upgrade system > From USB storage
16. The Android 9 image will be loaded into the headunit.

You can follow this video as well : https://www.youtube.com/watch?reload=9&v=EhEdeD5RICk

b) if you dont have a sdcard slot or previous metod does not work for you as your sdcard slot is just an USB extension
b1) By means of ModInstaller apk made by Hal9k
This is the easiest way for those who don't have sdcard slot.
Instructions here --> http://hal9k.ru/?page_id=207
b2) By means of OTG Cable

1. This procedure requires some kind of soldering knowledge and Android knowledge.
2. You must need a OTG USB cable (build your own) as per the following post:
   https://forum.xda-developers.com/an...px3-5-headunit-mod-recover-flash-som-t3766892
3. Download Hal9k_Mod_3.x_upgrade_to_Android_9.0.rar and look for sdupdate.img file
4. Download BatchTool_1.7 or AndroidTool 2.39 from this post and download Drivers from this URL
5. Install the corresponding Drivers (select x86 or x64 depedning on your Windows version)
6. Open your Headunit and extract the PX5 SOM from the Motherboard
7. Connect the OTG USB cable into the PX5 SOM as per the previous thread and to the PC
8. Execute BatchTool.exe or AndroidTool.exe. In AndroidTool go to the Firmware Updte tab
9. The app will inform you that a USB is detected .
10. Load the sdupdate.img file on Firmware (FW) option
11. Press Upgrade button
12. When Upgraded...plug again the SOM into the Headunit...
13. Start unit and ente into recovery...you will find a 9.x.x recovery version
14. Proceed with the system upgrade as previous section from a USB storage

Note: if the app does not detect any device, check the drivers are installed
If the device is detected as mass storage, press oer the switch button to change the mode to a loader (the mode for the device to receive a flash file)

Witson MTCE MX V3.30（with LOGO) and MX ROM 20190724

Hi everyone,

I got download links provided by Witson support for those files and wanted to share them, but my account is not allowed yet to post links:

To prevent spam on the XDA forums, ALL new users prevented from posting outside links in their messages. After approximately 10 posts, you will be able to post outside links. Thank you for understanding!

So, in the following links please replace PREFIX by https link on sendspace.com website

Source: MX
MTCE_MX_V3.30（with LOGO).rar: PREFIX/pro/dl/sp9kf6
hct4_PX5_9.0_ota(20190724）.zip: PREFIX/file/8p09b9

Useful Apps

Useful Apps for PX5 Android 9

MTCDialer 1.2.3 --> New Version for this app supporting for Android 9. Thanks @f1x & @scorillo_ro
https://github.com/scorillo/MtcDialer/releases/download/1.2.3/com.f1x.mtcdialer-1.2.3.apk
This app allows to Use Google Voice Assistant to Dial to your Contacts stored in your HeadUnit
To make a call just say a name of the contact stored in your PhoneBook, e.g. "Mom" or "Britney Spears" (if you have one ) or say some digits, e.g. "One One One Seven Six Five Four Two Zero"
No Internet Connection is required.