Enabling MTU above 1500 for S32G VNP RDB2

[achyu_m]

HW information: S32G VNP RDB2 (EVB)

BSP:  BSP_nxp-s32g-evb_br-710_be-710 (SVN941162_JBN31)

Hello Team,

Does the evaluation board mentioned above support jumbo frames transmission and reception?

I tried enabling jumbo frames with BSP provided from QNX as mentioned above, but was unable to increase the MTU size above 1500. Can you confirm if  above mentioned EVB support above 1500 MTU for jumbo frames.

[Daniel-Aguirre]

Hi,

PFE setup should be the same between QNX and the Linux BSP, for which packets up to 1522 bytes can be received and the MTU is always 1500 bytes.

Please, let us know.

[achyu_m]

Hi Daniel,

Thanks for the response. We are using GMAC Ethernet for our use case. 

In BSP, we tried setting MTU to 5000 by enabling jumbo frames as well as disabled store and forward mechanism, however MTU still remains unchanged at 1500.

Can I use the evaluation board S32G VNP RDB2 for Transmission and Reception of Jumbo frames for unsegmented 5000 bytes with GMAC? Also, Is there any possibility to enable jumbo frames in GMAC?

[Daniel-Aguirre]

Hi,

The following is said in the GMAC Subsystem Reference Manual [Page 777, GMAC Subsystem RM, Rev. 2, 03/2021]:

"Giant Packet
When this bit is set, it indicates that the packet length exceeds the specified maximum Ethernet size of 1518, 1522, or 2000 bytes (9018 or 9022 bytes if jumbo packet enable is set).
Note: Giant packet indicates only the packet length. It does not cause any packet truncation."

Also [Page 40, GMAC Subsystem RM, Rev. 2, 03/2021]:

"Jumbo Packet Enable
When this bit is set, the MAC allows jumbo packets of 9,018 bytes (9,022 bytes for VLAN tagged packets) without reporting a giant packet error in the Rx packet status.
0b - Jumbo packet is disabled
1b - Jumbo packet is enabled"

Meaning that the Jumbo packet enable bit should be set if packets up-to 9K bytes are to be received. Could be that only the Giant packet bit is enabled on the linux side.

Also, could be that both PFE and GMAC share configuration on Linux, hence the MTU limit.

Please, let us know.