Yokemate of Keyboards
Posts: 11609 from 2003/5/22
>> How many PCI lanes does the T4 support?
> AFAIK information about the number of PCIe (note the "e", legacy PCI is not supported)
> lanes is not public yet. What's been revealed is the number of SerDes lanes, of which
> some will be configurable as PCIe lanes (16 at best in case of T4240, 12 at best in
> case of T4160; but due to SATA controllers will have to be decreased by 1 or 2 in both
> cases), and the type and number of the PCIe controllers
According to http://www.freescale.com/files/training/doc/dwf/DWF13_APF_NET_T1284.pdf
(page 16), it's indeed possible with the T4240 to have up to 16 SerDes lanes for PCIe using either 2 controllers (x8 x8), 3 controllers (x8 x4 x4) or 4 controllers (x4 x4 x4 x4), whereas each controller can be downgraded to use less lanes. Those configurations would be without SATA though.
Using 2 lanes for SATA leaves 14 lanes for PCIe, which can be configured as using either 3 controllers (x8 x4 x2) or 4 controllers (x4 x4 x4 x2).
While two out of the T4's four PCIe controllers support PCIe 3 standard, the following restriction is mentioned by Freescale:
"8 Gbaud is not supported with x8 link width
This means that whenever a PCIe3-capable controller of the T4 is being assigned 8 lanes, it switches from PCIe 3 to PCIe 2 standard, reducing the bandwidth of those lanes to about a half.
has some more info on page 31/32:
Using 16 SerDes lanes for PCIe, the following configurations are possible:
1. x8-gen2 x8-gen2
2. x8-gen2 x4-gen3
x4-gen2 x4-gen2 x4-gen2