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Lacking support for A50 chipset #195
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Hi, this is simply because no one in possession of an A50 device (and there are not that many!) has ever bothered to send any patches. Since device support is purely community driven, without any interest and effort nothing will happen. |
Thanks for your answer! Many cheap generic tablet use chipsets like these. It probably comes down to: It's so cheap that no-one bothers to look at them development-wise. Anyways, I am in possession of 4 identical tablets. I do not have the original fw, neither can I find it on the internet. I asked their support and got a no. I unlocked and flashed another a50 fw on two of them and got a modified boot.img to boot with Magisk support and root it. Maybe this helps in acessing certain areas of the working tablets. Another one I bricked by selecting "multi partitions" in PhoenixSuit. I believe that using that check made it flash "sys_config" and messed up the display driver, since it's all white at boot, fading to black over time. Even all white, I can still feel the tablet booting, since eventually it responds to touches and power presses. I sent the bricked one into warranty, got it back reflashed and bricked it again the exact same way. This time I forgot to unlock the OEM switch, which apparently did "something". Exact same issue: Boots, but I cannot see anything. Regarding your question: I do not have a SPL to load. I tried to upload and execute several pointers using sunxi-fel, but most of the time the tablet would just lock up and I would need to reboot it. I remember using the official datasheet of the a50 a while back to try and get the right locations to load certain stuff, but even this made it lock up.
How do I do that, and what do I need to modify for it to work on the a50? I am dualbooting Ubuntu 20 and Windows 11, so I should have everything I need. Would the working rooted tablet help in detemining something? Even just backing up the working sys_config and loading it onto the bricked one would already help immensely. I can imagine more people having that exact dilemma. Any help is greatly appreciated! |
Hi Valentino, thanks for coming back on this. I heard of those A50 tablets, which might also explain the lack of community support, as tablets are harder to enable and also provide a less tempting development system, as graphics support is harder to set up in mainline Linux.
Do you have a serial console? Even tables typically have serial pins or at least pads, thought it requires opening it up. So there is certainly more to do, though we can definitely help you with that. Most peripherals in the A50 should be very similar, if not identical to ones already supported in mainline, so that's certainly helpful. And since we have the manual, we can fix up the rest. One big blocker is typically DRAM support, though we can work around this for the first time. I will have a look at the A50 memory map, and can then probably suggest a sunxi-fel patch, though there is typically some experimentation involved, to learn about the BROM stack location and other details. If you could do some test runs, that'd be helpful, will come back to you. |
Thank you for your time @apritzel. Let's do it. However, remember, the working rooted tablet isn't running the original fw but still works somehow. I think sys_config (or a partition) wasn't overwritten. Maybe this can dumped together with /sys/* ? Anyways...
Seems already mounted, as previous command worked.
If you need information about that, I will need some memory adresses to dump, as (your?) tool apparently needs some.
I opened it up and probed it with a multimeter and my FTDI 3.3V adapter on various test points across the board, but didn't find any active serial communication going on. If you still think there should be one, I can take a photo of the board for you to look around. EDIT: Maybe it is possible to craft a boot.img that dumps the serial console over some gpio or even to the external SD? EDIT2: peekpoke mentioned something on /proc/iomem, so I'm documenting this as well:
Again, thank you for your time! If there is anything additional to try, let me know! I'm open to run, try or diagnose additional stuff. |
@apritzel I'll need to send the bricked tablet into warranty asap, therefore if you want me to have a "thinker" unit (that we can flash, reflash, document and eventually even bring back to life) I need to know it in the next 1-2 days, since the warranty will run out if I don't. After I send it in, I will only have the working tablets where I wouldn't want to thinker with flashing anymore. :) |
Thanks for dumping the information, I will have a look in the next days (am busy with T113s enablement atm). So normally we don't need to flash anything for Linux enablement, it's actually easier and safer to do everything via SD card or via FEL. Typically most Allwinner boards boot from SD card, though there are exceptions. What would be good to retain is a tablet which boots some working vendor firmware, and which we can inspect, so is rooted. So that we can later learn about certain bits and settings that we didn't think of now. But we don't need to flash anything to this "information donor", so you could use it as a normal tablet. If the "bricked" tablet is just bricked in the sense that it doesn't boot the vendor firmware anymore, but at least goes into FEL mode: that's a perfect development vehicle. We will replace the whole software stack in the process, so don't need any of those bits. As mentioned, it is just helpful to have another device which still boots the vendor firmware. Regarding UART: typically there are even pins labelled RX and TX on most PCBs, so I'd say it's worth to have another look. It tremendously simplifies development. You can use the UART on the SD pins, but that requires a SD breakout board, and is somewhat fiddly to use if you need the SD card as well. If you can bring the tablet into FEL mode easily (a button?), then this could be a route to explore, since you then could dedicate the SD card slot to the UART. |
To create the hello-world binary, just use: I use this adapter for the PortF-UART: |
While working with an Allwinner A50 chipset I saw that there is basically nil support.
Even sunxi-fel doesn't recognize it. (0x1755)
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