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Apple's new dongle-happy MacBook Pros not fully compatible with Thunderbolt 3 peripherals

Well, this is a touch embarrassing. When Apple unveiled its latest MacBook Pro hardware a few weeks back, it declared that USB-C-compatible Thunderbolt 3 ports (and lots of dongles) were the future of the company’s Mac division. We disagreed with that decision, while acknowledging that yes, Apple does have a long history of sunsetting old standards and introducing new ones ahead of the rest of the industry (whether or not this situation is analogous is a topic we discussed). Now, news has surfaced that Apple’s newest MacBook Pro hardware may not be compatible with Thunderbolt 3 peripherals already on the market.

First, some context: Thunderbolt 3 is the third iteration of Intel’s Thunderbolt interconnect standard and is the first version of that standard to be physically compatible with USB Type-C connectors. It debuted in early June 2015, and support began shipping with Skylake hardware towards the end of last year. Thunderbolt 3 is used in the external GPU XConnect standard jointly developed by Intel, AMD, and Razer. It’s USB-C compatible (an extremely smart move from Intel) and should be a plug-and-play solution for Apple’s MacBook Pro. After all, Thunderbolt 3 is Thunderbolt 3… right? Apparently, no — not when Apple deploys it.

Thunderbolt-External

According to peripheral manufacturer Plugable, Intel’s Thunderbolt 3 standard specifically calls for certain TI chips to handle power delivery and alternate mode negotiation. The chip specified by Intel, and used by Plugable (and possibly the entire rest of the industry) is the TPS65982. It’s described by Texas Instruments as: “a stand-alone USB Type-C and power delivery (PD) controller providing cable-plug and orientation detection at the USB Type-C connector. Upon cable detection, the TPS65982 device communicates on the CC wire using the USB PD protocol. After successful USB PD negotiation is complete, the TPS65982 enables the appropriate power path and configures alternate mode settings for internal and (optional) external multiplexers.”

According to Plugable, none of its existing hardware currently on the market is compatible with the MacBook Pro because OS X expects all devices to use the second-generation TPS65983 solution. Here’s how the company describes the problem:

The version of OS X on the new MacBook Pros (late 2016) will not work with existing Thunderbolt 3 docks and adapters that were certified for Windows prior to the release of the MacBook Pro. These existing devices use first generation of TI USB-C chipset (TPS65982) in combination with Intel’s Thunderbolt 3 chipset (Alpine Ridge). Apple requires the 2nd generation TPS65983 chipset for peripherals to be compatible. Certification of solutions across different device types is still in-progress for this 2nd generation chipset. From the Plugable product line, our dual display graphics adapters for DisplayPort and HDMI (TBT3-DP2X and TBT3-HDMI2X) are affected… We’ve also postponed our TBT3-UD1 Docking Station to update to the TPS65983 chipset and re-certify to make this docking station MacBook-compatible. Our Flagship TBT3-UDV dock with Power Delivery/Charging was already planned to use the next generation controller chip from TI, and will be compatible with the 2016 Thunderbolt 3 MacBooks.

Plugable’s Joshua Henry offered some additional information in a follow-up thread response. “The Intel reference design calls for the use of the TI chipset to handle Power Delivery and Alternate Mode negotiation. The Intel Thunderbolt 3 chipsets cannot do this on their own, or if they can, it hasn’t been implemented yet. To our knowledge, all current Thunderbolt 3 products incorporate the TPS65982 chipset into their design and will be incompatible with the new MacBook Pro until new versions with the TPS65983 are released.”

We’ve got questions in to Intel about this, but here’s what we know thus far. First, this problem appears to be specific to Thunderbolt 3 peripherals. If you have a Thunderbolt 2 device plugged into a Thunderbolt 3 port via an adapter, it seems to work fine. That limits the amount of hardware likely to be incompatible, since not that many Thunderbolt 3 peripherals have been built yet.

The flip side to this, however, is that Apple appears to have asleep at the switch when it comes to the hardware already on the market. It’s one thing to be on the cutting-edge of technology, but declaring that your users are all expected to convert to a new cable standard while simultaneously releasing hardware incompatible with all of the Thunderbolt 3 hardware currently on the market is really, really dumb. What happens to Apple buyers who pulled the trigger on a MacBook Pro and some new Thunderbolt 3 peripherals at the same time?

What makes all of this even stranger is that the hardware Apple isn’t supporting isn’t some random Thunderbolt 3 controller made by a third party. These are chips that are part of Intel’s own reference design for Thunderbolt 3 devices. A little digging on TI’s forums turned up several answers, including one from TI employee Brian Berner: “The TPS65983 is a special product for ThunderBolt 3 devices (for example: hard drives, docks, and monitors) that connect to ThunderBolt 3 hosts (such as tablets, notebooks, and workstations.)” That may be true, but Intel’s own release notes for its Thunderbolt 16.2.52.250 driver, released on 9/30, state: ” Added support for TI TPS65983 PD Controller in SW, SDK API and samples.” Other comments from various places in TI suggest that the TI TPS65983 controller wasn’t available until January 2016 at the very earliest. Development support for the chip was still limited to by request only as of April, and the configuration tools TI offers for other chips weren’t available until the very end of March.

In short, the bulk of the evidence suggests that full support for the TPS65983 controller has taken 6-10 months to appear and was only recently added to Intel’s own SDKs. It’s also unclear what the actual difference is between the two chips. I’m certain TI is right when it calls the 983 chip a “special product,” but I’ve paged through the data sheets for the 982 and the 983 and found nothing at all to distinguish them. They have identical circuit diagrams, identical layouts, and once you correct for some small variation in verbiage, identical features.

How many people are going to be harmed by this? Probably not very many. Thunderbolt 3 is new, the MacBook Pro is new, and new hardware variants will adopt the 983 chip. Nonetheless, this is something Apple could’ve entirely prevented by either supporting the 982 chip in macOS or simply telling people from stage that only new Thunderbolt 3 peripherals would be compatible with the MacBook Pro. But I suppose it was just easier to call the whole thing “courageous” and leave it at that. This isn’t going to put a shine on the new MacBook Pro systems, and it’s an absurd situation all around. The type of controller chip used inside a peripheral interconnect should be of absolutely no regard to anyone looking for a new laptop. Having to juggle which hardware is compatible with which systems when they all support the same standard is absurd. Hopefully Apple will patch support for the TPS65982 chip into macOS.

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