If you ever try to install more than one DeckLink or Intensity PCIe card you might stumble upon a problem – each card will work totally fine separately, but once you install more than one card all of them will stop working. This configuration is officially supported by BMD and should work, but in some cases it just does not. Why?
Luckily, we were not the only ones having this issue. Thanks to helpful responses on the forum, we were able to quickly deduce that the issue is in fact in PCIe cards made by BMD. And indeed, after a few minutes with a soldering iron we were able to make all our cards work at the same time.
In other words, good news! You can easily fix the design mistake yourself and get your cards to work. This will likely void your warranty, which is unfortunate given that BMD knowingly sold you a flawed card. They are also suspiciously silent about the issue, we even asked their support about it but received no response whatsoever. Interesting.
Check out the pinout of a PCIe slot. There is not much that can go wrong there. For example, SMBus pins are not even routed on most of the cards, so you can ignore them. You are left with just data lines, power pins, PERST and a few other pins. PERST is the problem. When investigating what PERST is supposed to do, you can stumble upon this helpful ticket. Basically, it is a discussion about a design of some PCIe card, and the idea is that a 10kΩ pull-down resistor on PERST is too much, and you need a higher value (like 100kΩ or so).
We located the PERST pin on our Intensity Pro 4K and DeckLink Mini Recorder 4K cards, followed the traces and found pull-down resistors on both cards. Their value? 10kΩ. Bingo!
You may be wondering why it works fine in some cases. For example, multiple BMD cards do indeed work OK on some motherboards, but not on others. And each card works fine individually, at least in most of the setups. Here is where it gets interesting.
In some configurations, the PERST line is shared between multiple PCIe slots! This is the case with some motherboards where PCIe slots do not have native CPU lanes, but rather go through the chipset. This can also happen if you are using PCIe bifurcation. In other words, there are many valid reasons why you can end up with a shared PERST line in your setup.
However, when this happens, it means that both pull-down resistors are
now in parallel. We can calculate the equivalent resistance in such
case: 1/R = 1/R₁ + 1/R₂. For two resistors that are 10kΩ we get
5kΩ equivalent resistance. If 10kΩ pulldown is wrong by itself, then
5kΩ is even worse. That is, the more BMD cards you have installed on
PCIe slots with a shared PERST line, the more likely you are to face
the issue. For most users the threshold will be at 2 cards. Essentially,
it pulls the PERST line to ground without letting it to go up,
meaning that your cards will always be in the reset state.
Yes! You can test this by putting one of your BMD cards into the main GPU slot (and placing your GPU into any other PCIe slot that can fit it). You will see that both Decklink/Intensity cards work fine in this configuration. That said, it is very likely that you do not want to use a setup like this in production, because using your GPU in any other slot except the one with x16 CPU lanes can possibly affect your GPU performance. If you need another confirmation, you can try using any other properly designed card together with your BMD cards, and everything will work fine, it is only the cards made by BMD that “conflict” with each other.
Fixing it is easy, you just need to remove the pull-down resistor on one of the cards (or all of them, which is what we do). Just find the resistor and use your soldering iron to remove it.
Here are some photos of the cards we fixed.
| Card | Photo |
|---|---|
| Intensity Pro 4K |  |
| DeckLink Mini Recorder 4K |  |
No. It is a hardware issue. You cannot fix it with a driver or software update. Once you plug in both of your cards they end up in the reset state, the motherboard is unable to enumerate them. There is nothing you can do besides removing or replacing the resistor that should not have been there in the first place.