We have the following interrupts: MSI, MSI-X and INTx. What do these different type of interrupts do in PCIe? I only need a short description. I only know that in PCIe interrupts are generated as packets when they are to be asserted and also when they are to be deasserted and that MSI and MSI-X exist for legacy support. I could be wrong. Is it possible to get answer to this very specific question on this forum?
Electronic – What do the different interrupts in PCIe do? I referring to MSI, MSI-X and INTx
interruptspcie
Related Solutions
Normally you would set up the SPI peripheral once, then leave it on. The extra handshaking you are doing is preventing you from using the hardware to its full capability. Also doing a busy wait for the master to assert slave select is a bad idea if you ever want the processor to do something else.
Since you are transferring 16 bits of less per message, I would just let the hardware take care of it. Then you can monitor the SPI interrupt flag to determine when new data has been received from the master. If you need to slow down the master for flow control reasons, I would do that outside of the SPI message. I suspect the interrupt is adding latency to your home grown handshaking scheme, and something somewhere isn't quite right and can't tolerate that latency. That's assuming of course that the interrupt doesn't try to touch the SPI hardware or any of its I/O lines.
Looking through the datasheet it looks like the CC6678 can operate in root complex mode so you should be able to connect the two. I did a similar board for testing a large batch of pcie cards.
Lanes
If I were going to try it I'd start with a 4 layer board. You're going to want nice 100Ohm differential pairs to connect your lanes together. It only supports 1 or two of them so that shouldn't be a problem. Just run them over a GND plane on layer two. Just follow good practice here for routing HS signals. Oh and Tx -> Rx, and watch your polarities :)
Clock
I saw the clock generator you picked from your other post, I'd probably put a 1->2 fanout buffer and drive one to each of your pcie slots.
Reset
You're going to need to generate a reset pulse for the cards as usually the mother board would do that. You could just slap down a simple supervisor that monitors 12V and tie it's reset output to both connectors. Maybe add a pushbutton too so you can reset manually during debug. I used a Linear LTC2916CDDB-1#TRMPBF.
Power
You're going to need 12V and 3.3V to power the connectors. I just used a standard desktop pc power supply because I had a bunch and they're easy to get. I just used a standard mother board power supply connector (Molex 44206-0007) and I put a little toggle switch from PS_ON to GND to turn things on and off. Oh and throw in a few 100uF tantalums on each rail for good measure.
Don't be nervous keep the lanes short, match the impedances and you should be fine.
Here's a pinout if you need one:
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Best Answer
[You should probably proceed straight to Frr's answer which is more accurate and provides much more background and context]
All the interrupts perform the same function: a notification about some event which is sent from one (PCIe) agent to another.
Why do we call these notifications "interrupts"? Well, in general (not always though), the micro-processor which gets interrupted would stop its current activity, save the state of this activity in some manner, and switch its attention to handling the interrupt (by means of executing Interrupt Servicing Routine; in short - ISR). We say that the arrival of this notification interrupted the normal flow of micro-processor, hence the name "interrupt".
In the early days, all interrupts were just wires: each event which had to be communicated between agents was represented by a single wire. However, as the number of such event grew, the number of wires which had to be routed on a chip became huge.
The introduction of standardized interconnects (PCI, PCIe, and more) between HW modules allowed a new concept for interrupts delivery to be used - a Message Signaled Interrupt (MSI). Why MSIs are better than just wires? Well, engineers though that if there is anyway an interconnect which allows for exchange of generic messages between agents, then it will be a waste of space to add unnecessary wires on top of it - you can use the existing interconnect in order to exchange special messages, just make sure that all agents treat these special messages as interrupts.
PCI MSIs were introduced in PCI2.2 (Wiki) as an alternative to the regular interrupts, and they became mandatory in PCIe.
MSI-X is just an extension of PCI MSIs in PCIe - they serve the same function, but can carry more information and are more flexible. NOTE: PCIe support both MSI and MSI-X.
The concept of MSI is very handy and allows for great reduction in wires routed on a chip, but it has few disadvantages:
Engineers who worked on PCIe spec were clever enough to foreseen that the above issues will become of major importance in the future. They decided to keep an option of using "legacy" interrupts - simple wires. These are INTx interrupts: in special circumstances a PCIe agent may be configured to use a simple wire instead of MSI to signal an interrupt. PCIe defines up to 4 wires per agent - these are named A-D. INTx is a general name for all four of them (x = A or B or C or D).
The main usage of INTx signals is to signal interrupts while the main PCIe interconnect is powered down: when agent needs to communicate, it "asserts" one of INTx, which causes the PCIe interconnect to be powered up.