[Rpcemu] A pleasant blue window...

Ralph Corderoy ralph at inputplus.co.uk
Sun Mar 21 17:33:44 PDT 2010

David wrote:
> The 3.71 rom works, as does the 'vanilla' 3.70 rom image I extracted
> from this RPC after a power on with shift & * (??) held down - the
> sha1sum of which equalled that of Ralph's so I know it's okay.
> At least this long sorry saga has highlighted the possible problem of
> patched rom images causing startup errors, and possibly running
> errors.

My guess is the blue screen is RISC OS detecting that some internal
checksum on the ROM isn't correct during POST.  That vaguely rings a
bell on other earlier emulators.  (So much gets learnt, forgotten, and
has to be re-learnt!)  Perhaps it needs to be mentioned somewhere in the
rpcemu FAQ/troubleshooting section?  Along with a link to known good
SHA1 digests.  :-)

Would it be nice if rpcemu looked at the ROM image provided and gave a
warning it if wasn't recognised?  Digging out the "MOS Utilities"
version and seeing if that matched the expected CRC-32-IEEE 802.3 may
stop these kind of issues.  I say CRC-32 rather than SHA1 because it's
still good enough but much easier to compute in code.  And it's what the
POSIX cksum(1) command gives too.

    $ cksum *
    1806840565 4194304 david
    212344744 4194304 davidwife
    2820737424 4194304 musus
    2453876003 4194304 mybad
    3184921365 4194304 mygood
    3728305141 4194304 rolf3.60
    4102711502 4194304 rolf3.71


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