Can max payload size in Device_Capabilities_Register be re-set?

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Can max payload size in Device_Capabilities_Register be re-set?

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zy_mooncity
Contributor III

Hi folks,

In PCIE specification, the max payload size can be one of these:

  • 000b = 128 bytes max payload size

  • 001b = 256 bytes max payload size

  • 010b = 512 bytes max payload size

  • 011b = 1KB max payload size

  • 100b = 2KB max payload size

  • 101b = 4KB max payload size

  • 110b = Reserved

  • 111b = Reserved

The max payload size field in LS1046A is 001, which is 256bytes.

In my scenario, two LS1046A boards are across connected for data transfer.  One LS1046A acts as RC, the other acts as EP. In order to improve the throughput, can the field be set to other value larger than 256bytes, take example, 101b for 4K bytes?

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r8070z
NXP TechSupport
NXP TechSupport

It is impossible set to other value larger than 256bytes in the LS1046 PCI Express Device Capabilities Register.

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zy_mooncity
Contributor III

Thanks for the answer.

I just assume some read-only fields can be modified temporarily by operating DBI Read-only Write Enable Register.

So it's a design restriction for LS1046A PCI controller, and only 256Bytes capability is provided, right?

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r8070z
NXP TechSupport
NXP TechSupport

Yes, it is right.

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