Overview of Timing Requirements for NXP QorIQ LS Processors

IDT provides a brief tutorial on the timing solutions required for NXP (Freescale) QorIQ / Layerscape processor-based systems.

Presented by Ron Wade, PCI Express timing expert. For more information about IDT's timing solutions, visit www.IDT.com/go/clocks.


Hi there, this is Ron Wade with IDT and today we're going to talk about NXP, formerly known as Freescale, CPUs. Specifically the QorIQ and Layerscape CPUs and the timing requirements that they have. So, it's basically divided into a couple of parts here. There's some timing that the CPU itself requires and then there's timing that depends upon your system and the number of SerDes links you have in your design and in your CPU. So, if we talk about the CPU part itself, we have the CPU cores which get a clock, and we have the memory controller inside the CPUs which gets a clock as well. And the memory controller clock is called the DDR clock. The CPU clock is called the SYS_CCB clock in the Freescale nomenclature, excuse me, the NXP nomenclature and those frequencies - they're single-ended clocks and they range, like the DDR from 66.66 MHz up to 100 MHz, and the CPU clocks range from 66.66 up to 133.33 MHz, in some cases. Those are single-ended LVCMOS input clocks. Additionally, some of the CPUs have a USB interface which may require a 24 MHz single-ended clock. And there's also an Ethernet interface built in, a one-gigabit Ethernet interface, that is, takes a 125 MHz single-ended clock as well and that's at 2.5 volts.
So, in the Layerscape series of CPUs which are based on the ARM core, Freescale has put into them, what they call a reduced oscillator mode where all the clocks over here basically are reduced by a single differential 100 MHz non-spreading clock, and this saves you from having to figure out and generate all these clocks. However, it has to be non-spread because the USB clock is also derived from it, so, if you're planning to use spread spectrum, you really can't use this mode. And, currently, it's only available in the Layerscape devices, not the legacy QorIQ devices.
So, that's the basics for the CPU and the memory controller. Then the SerDes is really dependant upon the particular CPU you're using and how many SerDes lanes you need in your design. So, the SerDes clocks, on the other hand, basically range from 125 MHz differential clock for Gigabit Ethernet, if you're using 10 Gigabit Ethernet, a 156.25 MHz clock is required. And then if you're using PCI Express, you'd use a standard 100 MHz PCI Express clock. All these happen to be differential and the number of SerDes lanes and their capabilities depends on the CPU you're using. So, this gives you an outline of how to just do a quick tally of what kind of clocks you need and in another video, I'll talk about the solutions that IDT has for NXP's devices.