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Entry  05 Jan 2016, Tom Stuttard, Suggestion, 64 bit bank type 
    Reply  05 Jan 2016, Konstantin Olchanski, Suggestion, 64 bit bank type 
       Reply  19 Jan 2016, Tom Stuttard, Suggestion, 64 bit bank type 
Message ID: 1155     Entry time: 19 Jan 2016     In reply to: 1153
Author: Tom Stuttard 
Topic: Suggestion 
Subject: 64 bit bank type 
> > I've seen that a similar question has been asked in 2011 but I'll ask again in 
> > case there are any updates. Is there any way to write 64-bit data words to MIDAS 
> > banks (other than breaking them up in to two 32-bit words, such as 2 DWORDs) 
> > currently? And if not, is there any plan to introduce this feature in the future?
> There is no "breaking them up" as such, you can treat a midas bank as a char* array
> and store arbitrary data inside. In this sense, "there is no need" for a special 64-bit bank type.
> For endian-ness conversion (if such things still matter, big-endian PPC CPUs still exist), single 64-bit 
> word converts the same as two 32-bit words, so here also "there is no need", once can use banks of 
> DWORD with equal effect.
> The above applies equally to 64-bit integers and 64-bit double-precision IEEE-754 floating point 
> numbers.
> But specifically for 64-bit values, such as float64, there is a big gotcha.
> The MIDAS banks structure goes to great lengths to make sure each data type is correctly aligned,
> and gets it exactly wrong for 64-bit quantities - all because the bank header is three 32-bit words.
> bankhheader1
> bh2
> bh3
> bankdata1 <--- misaligned
> ...
> bankdataN
> bh1
> bh2
> bh3
> banddata1 <--- aligned
> ... etc
> So we could introduce QWORD banks today, but inside the midas file, they will be misaligned defeating 
> the only purpose of adding them.
> I guess the misalignement could be cured by adding dummy words, dummy banks, dummy bank 
> headers, etc.
> I figure this problem dates all the way bank where alignement to 16-bits was just getting important. 
> Today, in the VME word, I have to align things on 128-bit boundaries (for 2eSST 2x2 DWORD transfers).
> So back to your question, what advantage do you see in using a QWORD bank instead of putting the 
> same data in a DWORD bank?
> K.O.

Thanks very much for your reply. I have implemented your suggestion of treating the 64-bit array as a 32-bit 
array for the bank write/read and this solution is working for me.

Thanks again for your help.
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