[c-nsp] flash checksum

[Randy Bush]

image in flash that's been there since 1948 seems to have bit rot

    System flash directory:
    File  Length   Name/status
      1   7390256  /c2500-k4p-l.120-21.S1  [invalid checksum]

and a tftp of same gets

    Copy 'c2500-k4p-l.120-21.S1' from server
      as 'c2500-k4p-l.120-21.S1' into Flash WITH erase? [yes/no]yes
    Erasing device... eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee ...erased
    Loading c2500-k4p-l.120-21.S1 from 147.28.0.39 (via Ethernet0): !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    COPY: Bad image - possibly corrupted

    COPY: Text checksum verification failure

    TFTP from TFTP.PSG.COM failed/aborted

    Verifying checksum...  invalid (expected 0xA6D3, computed 0xDBFD)
    Flash copy took 0:00:09 [hh:mm:ss]

and

    tftp.psg.com:/tftpboot> cksum c2500-k4p-l.120-21.S1
    475257926 7390256 c2500-k4p-l.120-21.S1

how the heck is the 2511 computing the checksum?

do i just assume bad flash and go get some?

randy