i9500 (Galaxy S4)

Added by steve . about 5 years ago

Has anyone evaluated the i9500 in depth? I obviously like the newer specs compared to the i9300.

It seems to still have an Exynos processor, which implies the modem might be isolated. This is my #1 concern.

Looking through its CM11 proprietary-files.txt, I see the firmware blob for audio codec as mentioned in the i9505 thread. I personally view proprietary firmware similar to proprietary silicon, and I would use wifi/bluetooth blob on Replicant, but realize the project stance is a bit different.

Other than those, it seems to have the usual closed libraries that could be stripped out. For my use, I don't even necessarily require the cell radio (mifi instead), but that option would be nice and I would imagine it would be necessary for official Replicant support.

Replies (9)

RE: i9500 (Galaxy S4) - Added by steve . about 5 years ago

The only information I can find mentions X-GOLD636 (PMB9820) for both the i9500 and SM-G900H (S5). The i9300/i9100 are XGOLD626, so I'd guess the 636 is an incremental upgrade that wouldn't be hard to make work with Replicant.

I found a block diagram in a business presentation ( p63/p69) where the baseband processor's main RAM is contained in the same package as the eMMC flash.

However, the million dollar question is what the heck that interface between processor/cell modem actually looks like! I can't find a data sheet for XGOLD636. I found a torrent of some 626 information at xda-developers that mentions AHB/AXI buses, which seem like common ARM things. I could dig into that to see what power the slave has, but I'm not entirely sure that's even the correct interface, or what else might be going on between the chips.

What was done to investigate the i9300's isolation? There's obviously a scale from "does not use snapdragon" to "ongoing randomized reverse engineering of PCBs", with the Replicant due diligence being somewhere in the middle. It would be nice to see the specifics on the wiki.

RE: i9500 (Galaxy S4) - Added by Paul Kocialkowski about 5 years ago

Well I'm a bit worried about the huge screen resolution, it may be too slow. I think modem isolation could be good, I'd have to look in-depth and do a proper evaluation. It would be a shame if audio was to require loaded firmwares, but that's not a show-stopper. The bootloader is certainly signed and non-free, as usual.

RE: i9500 (Galaxy S4) - Added by steve . about 5 years ago

I went ahead and got one. What I really wanted was a wifi-only tablet, but I couldn't find anything that would fit in my pocket and had a modern amount of RAM.

I didn't look close enough to realize Cyanogenmod is still only releasing nightlies (if it follows the S3 schedule then a snapshot will drop in January?). It is a CM11 only device which implies a future Replicant 4.4 (and why would CM backport?) so perhaps the project isn't ready for that.

It's currently running a CM11 nighty, with a Debian installation along side (no SIM card, so no idea about radio functionality). I'll probably take a look inside some time, but wait to start fooling with removing proprietary software bits until CM stabilizes.

Is there a general Replicant porting guide somewhere? How do most Android apps react when you start removing eg 3d graphics libraries?

RE: i9500 (Galaxy S4) - Added by Paul Kocialkowski almost 5 years ago

Indeed, the Galaxy S 4 (I9500) won't be supported in Replicant 4.2, but if it could make an interesting target for 4.4, it's worth taking a good look at it.

Is there a general Replicant porting guide somewhere? How do most Android apps react when you start removing eg 3d graphics libraries?

Well, it's more complicated than that, you have to somewhat adapt the rest of the system to handle the lack of graphics acceleration as best as possible, so it involves code changes (that are specific to each version of Android apparently) and hence rebuilding the image from scratch. Just taking CM a removing a few libraries won't do.

RE: i9500 (Galaxy S4) - Added by Paul Kocialkowski almost 5 years ago

In the meantime, could you provide some radio logs: adb logcat -b radio? and perhaps dmesg too.

RE: i9500 (Galaxy S4) - Added by Kurtis Hanna about 1 month ago

I think that the exynos versions of the Galaxy S4 and the Galaxy S5 are the last versions in the Galaxy S series that still have decent modem isolation.

RE: i9500 (Galaxy S4) - Added by Jack K 29 days ago

Hi Kurtis,

What makes you think that later Galaxy S series phones with Exynos SoCs have poor modem isolation?



RE: i9500 (Galaxy S4) - Added by Kurtis Hanna 29 days ago

Hi Jack,

Thanks for your question. The Exynos version of the Samsung Galaxy S6 uses the Exynos7420 SoC, which has a LTE Modem on the SoC itself.

All Galaxy S series phones that came after this one also has a LTE modem on the SoC. It is my assumption that if there is a modem on the SoC it isn't isolated to the degree that Replicant requires.


RE: i9500 (Galaxy S4) - Added by Andrés D 29 days ago

They maybe have IOMMU like recent Qualcomm SOCs have. GrapheneOS uses that IOMMU to isolate radios (NFC, Wi-Fi, Bluetooth, Cellular), among other hardware like GPU, media engine, image processor, etc.

Before considering the modem correctly isolated, we need to investigate if IOMMU exist and how to configure it to not allow the modem access the RAM freely.