[U-Boot-Users] Multicast TFTP problems

[Ben Warren <bwarren@qstreams.com>]

Rafal,

Rafal Jaworowski wrote:
> Dave,
>
> I'm having problems with tftp transfer with current U-Boot running on 
> MPC5121 (FEC controller); since your mcast tftp implementation we first 
> attempt to transfer using some bigger blocksize:
> #define TFTP_MTU_BLOCKSIZE 1468, and it seems my problems are related to 
> this size.
>
> When running current code (ET_DEBUG enabled) it fails like the following:
>
> => run load
> Using FEC ETHERNET device
> TFTP from server 192.168.1.1; our IP address is 192.168.160.77
> Filename '/tftpboot/ads5121/u-boot.bin'.
> Load address: 0x100000
> Loading: send option "timeout 5"
> Got OACK: timeout 5
> Blocksize ack: 1468, 1468
> T T T T T T T T T T
> Retry count exceeded; starting again
> Using FEC ETHERNET device
> TFTP from server 192.168.1.1; our IP address is 192.168.160.77
> Filename '/tftpboot/ads5121/u-boot.bin'.
> Load address: 0x100000
> Loading: send option "timeout 5"
> Got OACK: timeout 5
> Blocksize ack: 1468, 1468
>
> Abort
> =>
>
> It fails with TFTP_MTU_BLOCKSIZE values above 1454, but it's ok with 
> anything up to this (including 1454):
>
> => run load
> Using FEC ETHERNET device
> TFTP from server 192.168.1.1; our IP address is 192.168.160.77
> Filename '/tftpboot/ads5121/u-boot.bin'.
> Load address: 0x100000
> Loading: send option "timeout 5"
> Got OACK: timeout 5
> Blocksize ack: 1454, 1454
> ###########
> done
> Bytes transferred = 157720 (26818 hex)
> =>
>
> Any hints on these observations? What might be going wrong here?
>
> kind regards,
> Rafal
>   
TFTP packets are structured as follows:

| Eth header (14 bytes) | IP header (20 bytes) | UDP header (8 bytes) | 
TFTP message | Eth FCS (4 bytes) |

You can see that the total overhead is 46 bytes. If your network port's 
maximum MTU size is 1500 bytes (the default), the math works out for a 
maximum TFTP PDU size of 1454 bytes.

However... the Ethernet header/trailer is not supposed to be included in 
the MTU. I suspect we have a terminology problem here. Let me dig a bit 
further to find out what's going on.

regards,
Ben