[Tinkerphones] MIPS CREATOR CI20

[Paul Boddie]

On Wednesday 27. March 2019 08.26.29 H. Nikolaus Schaller wrote:
> 
> > Am 25.03.2019 um 11:55 schrieb Paul Boddie <paul at boddie.org.uk>:
> > 
> > Yes, I have a CI20 board.
> 
> Ah, great!

I may have mentioned it before somewhere, maybe not on this list, though.

[...]

> > Apart from that, I have used the Debian GNU/Linux distribution on the
> > CI20, but since I don't care about the GPU (and don't like proprietary
> > drivers/firmware),
> 
> Yes, I don't as well, but if it is the only choice, I am not that
> ideological... Anyways there is the GPLed kernel driver which I am
> currently interested in.

It would actually be interesting to make alternative firmware, and I think 
efforts have been made for other GPU technologies in this regard, but it 
requires a lot of time and reverse engineering plus familiarity with the 
technologies involved.

But even with GPL-compatible kernel drivers, these proprietary GPUs cause 
considerable problems, although I am surely telling this to someone who 
already knows about the practical difficulties they cause. :-)

> > I haven't used it with the GPU enabled. On some occasions, I have used it
> > as a desktop system, but more often I log into it across the network.
> 
> That is like what I do with a Letux Cortex 8 and a RasPi 3B+. Just to habe
> specific compute power for special tasks. For example debootstrapping the
> LetuxOS rootfs images.

Right. Indeed, I should use it a bit more for building things, and I think the 
power consumption is pretty good, although I haven't measured it. One thing 
that disappointed people was the wired network performance, recalling the 
reaction from the OpenWrt community. (I also haven't tried the wireless 
network support because that involves another binary blob.)

[...]

> > I then used a later kernel (3.18 instead of 3.08) for which the supplied
> > GPU drivers probably wouldn't work, anyway, and I didn't fetch newer
> > ones. Of course, Imagination have dropped the CI20 completely, so the
> > links on elinux.org do not work (as you probably saw already):
> > 
> > https://www.elinux.org/CI20-SGX_kernel_module
> 
> Yes. I have already been able to find a copy of the DDK1.14 files.
> 
> Comparing with the TI provided DDK1.14 shows that they are almost the same,
> except that TI added better OMAP support than the IMG package. But there
> are ca. 15 code changes in general code which will become interesting to
> study.

I should probably take a look. I have occasionally browsed the documentation 
for PowerVR in case there were some helpful things released that might make 
improved Free Software support possible, but I don't really have a focus on 
this kind of thing.

[...]

> > I tend to use SD cards for new installations, however, leaving the flash
> > memory alone.
> 
> Yes, that is probably not a big issue then.
> 
> A question about the SD format for the non-Flash case: does it also have the
> standard 2-Partition scheme (FAT for u-boot and uImage and DTB) plus an ext
> for rootfs?

The instructions I followed are here:

https://www.elinux.org/CI20_Dev_Zone#Making_a_bootable_SD_card_from_sources

I don't think the FAT partition is needed. On one of my cards, I just have a 
single "Linux" partition:

Device     Boot Start      End  Sectors  Size Id Type
/dev/sdc1        4096 15278079 15273984  7.3G 83 Linux

And the partition uses the ext4 filesystem. So it is a similar arrangement to 
that supported by the Ben NanoNote, with the difference being that the 
NanoNote has a modified U-Boot in the flash memory that understands ext2/3/4 
to access the SD card, whereas the process is supported directly by the CI20 
hardware by changing a "jumper" on the board.

(It's possible that the JZ4720 on the NanoNote might also support booting to 
SD, but it could be a feature of newer SoCs. The JZ47xx series support booting 
over USB in the SoC which is also a possibility with the CI20.)

> Then we might be easily able to have makesd support the CI20 as well.
> 
> If it uses a hidden section for binary U-Boot and/or kernel it is also
> possible but a little more tricky and more difficult to maintain.
> 
> So it is good to know that you have such a board an might be able to help
> testing or setting up another one.

As far as I remember, it is all rather transparent. There is no special FAT 
boot partition like on the Letux 400, and the uImage just lives in /boot in 
the main partition. U-Boot itself gets installed into a specific region near 
the start of the disk, but I don't think this is particularly exotic.

Paul