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Cache Problem on TQ850


Title: Cache Problem on TQ850
Cache Problem under eCos on TQ850

 

 

The hardware set up being used is a PowerPC 850.

 

The following packets are SNMP responses to a GET command on an OID .2.16.44.1.4.1.1.4.1.1.3.1.2.0  .   The previous two gets also failed with the Text message being send over the network having the same error as shown here the correct value is "Bit0-CByte_str" and for the error the string is shown as "Bit0-Cbyteescr".   From other runs the text message returned is combined with the text of previous OID strings.

 

This is the first failure, with the UDP check sum failing as the text has been changed.

 

User Datagram Protocol, Src Port: snmp (161), Dst Port: 4050 (4050)

    Source port: snmp (161)

    Destination port: 4050 (4050)

    Length: 78

    Checksum: 0x35a9 (incorrect, should be 0x40a9)

Simple Network Management Protocol

    Version: 1

    Community: public  

    PDU type: RESPONSE

    Request Id: 0x6d4dc731

    Error Status: NO ERROR

    Error Index: 0

    Object identifier 1: 2.16.44.1.4.1.1.4.1.1.3.1.2.0

    Value: OCTET STRING: Bit0-CByteescr

 

 

0000  00 30 05 19 b8 f9 00 d0 93 00 1f 80 08 00 45 00   .0............E.

0010  00 62 34 eb 00 00 40 11 43 cb 89 df 98 d5 89 df   .b4...@.C.......

0020  55 41 00 a1 0f d2 00 4e 35 a9 30 82 00 42 02 01   UA.....N5.0..B..

0030  00 04 06 70 75 62 6c 69 63 a2 82 00 33 02 04 6d   ...public...3..m

0040  4d c7 31 02 01 00 02 01 00 30 82 00 23 30 82 00   M.1......0..#0..

0050  1f 06 0d 60 2c 01 04 01 01 04 01 01 03 01 02 00   ...`,...........

0060  04 0e 42 69 74 30 2d 43 42 79 74 65 65 73 63 72   ..Bit0-CByteescr

 

 

 

The second packet is successful the text message not being changed and the checksum is now correct.  Both packets have the data and request Id so the error can be seen to have occurred after the checksum calculations.

 

User Datagram Protocol, Src Port: snmp (161), Dst Port: 4050 (4050)

    Source port: snmp (161)

    Destination port: 4050 (4050)

    Length: 78

    Checksum: 0x35a9 (correct)

Simple Network Management Protocol

    Version: 1

    Community: public

    PDU type: RESPONSE

    Request Id: 0x6d4dc731

    Error Status: NO ERROR

    Error Index: 0

    Object identifier 1: 2.16.44.1.4.1.1.4.1.1.3.1.2.0

    Value: OCTET STRING: Bit0-CByte_str

 

 

0000  00 30 05 19 b8 f9 00 d0 93 00 1f 80 08 00 45 00   .0............E.

0010  00 62 34 ec 00 00 40 11 43 ca 89 df 98 d5 89 df   .b4...@.C.......

0020  55 41 00 a1 0f d2 00 4e 35 a9 30 82 00 42 02 01   UA.....N5.0..B..

0030  00 04 06 70 75 62 6c 69 63 a2 82 00 33 02 04 6d   ...public...3..m

0040  4d c7 31 02 01 00 02 01 00 30 82 00 23 30 82 00   M.1......0..#0..

0050  1f 06 0d 60 2c 01 04 01 01 04 01 01 03 01 02 00   ...`,...........

0060  04 0e 42 69 74 30 2d 43 42 79 74 65 5f 73 74 72   ..Bit0-CByte_str

 

 

When the cache is turned off this error is no longer seen,  when on about 3% of all packets were failing.  However with cache enabled the flood test did not generate any errors.

We are using the OpenBSD stack from a CVS snapshot taken a month ago. Does anyone know why enabling the cache would directly effect the upper layers of the protocol stack, and how to solve the problem?



Siemens Plc

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