PCIe Speed

Alican ESLEK

Hello,

I’m writing to get information about topic is related to speed of PCIe interface. We are using PCIe interface of C6678 DSP. We have configured DSP as Root Complex and FPGA as End Point.

In the RC mode, we have configured to Gen2 speed of PCIe by setting the DIR_SPD field to 1 in Gen2 register (PL_GEN2). But, when we read this register after setting, we realized that DIR_SPD bit in the Gen2 register is always 0. Also, we have read all bits in the Gen2 register correctly except DIR_SPD bit. According to PCIe user guide (Sprugs6c), DIR_SPD bit in the Gen2 register is read/write bit.

Why we don't read DIR_SPD bit in the Gen2 register correctly? How can we solve this problem?

Thanks & best regards

Alican

over 10 years ago

0 Ganapathi Dhandapani95 over 10 years ago

TI__Mastermind 28085 points

Hi Ailcan,

Switch between Gen1 and Gen2: set DIR_SPD (bit 17) in PL_GEN2 register to 0h (initialized at Gen1, default) , or set to 1h (switch to Gen2), before the link up

Please note that after you set the DIR_SPD=1 in PL_GEN2, you may not see the change in memory review (DIR_SPD still read back as 0 after link up). But you should be able to see the throughput difference.

Thanks,

0 Alican ESLEK over 10 years ago in reply to Ganapathi Dhandapani95

Intellectual 396 points

Hi Ganapathi,

Thanks for your reply. We want to detect speed of Pcie interface (Gen1 or Gen2) in our code. Could you suggest another way to determine speed of Pcie (Gen1 or Gen2) after link up?

Thanks again

Alican

0 Ganapathi Dhandapani95 over 10 years ago in reply to Alican ESLEK

TI__Mastermind 28085 points

Hi,

Although you set 1 to "DIR_SPD" field, it will not show being set after the initialization. Instead, you can check the "LINK_STAT_CTRL" register that "NEGOTIATED_LINK_WD" field will show the link width (lane number, 0x1=x1 lane, 0x2=x2 lane) and "LINK_SPEED" field will show the link rate (0x1=GEN1, 2.5Gbps; 0x2=GEN2, 5.0Gbps).

Thanks,

0 Alican ESLEK over 10 years ago in reply to Ganapathi Dhandapani95

Intellectual 396 points

Ganapathi,

Thanks for your quick reply and assistance.

Regards

Alican

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PCIe Speed