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Re: Altair Checksum Loader Bugs

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  • mfeberhard
    I saw this when I disassembled the loaders some years ago. (My disassebly of the 3.X and 4.X loaders are in the Files section.) I think this bug survived
    Message 1 of 4 , Mar 22 2:58 PM
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      I saw this when I disassembled the loaders some years ago. (My disassebly of the 3.X and 4.X loaders are in the Files section.) I think this bug survived because most people either loaded through the console (so the ports were the same) or had a parallel-port load device, such as an OP-80 reader. This bug would only be a problem if you loaded from the 2SIO serial port, but used some other port as your console - not too common a configuration.

      This is really easy to fix - the correct instruction sequence would be:

      IN SWTCHS
      ANI 01H ;SWITCH *A8* SPECIFIES STOP BITS
      RLC
      RLC ;PUT IN PLACE FOR SIO2WS1
      ADI SIO2DS1+SIO2WS3
      OUT SIO2C0

      (formatting mangled by HTML)

      This fix is nice because it is exactly the same length - so the three bytes that change could even be patched manually.

      You could easily fix this code, then create a new paper tape image with my MAKEALT utility.

      -Martin
    • Dan Roganti
      ... such as, a Teletype with a papertape option --the most common console of the day. The term bug being thrown around here is an outgrowth of the system
      Message 2 of 4 , Mar 22 3:22 PM
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        On Fri, Mar 22, 2013 at 5:58 PM, mfeberhard <eberhard@...> wrote:
         

        I saw this when I disassembled the loaders some years ago. (My disassebly of the 3.X and 4.X loaders are in the Files section.) I think this bug survived because most people either loaded through the console (so the ports were the same)


        such as, a Teletype with a papertape option --the most common console of the day.
        The term bug being thrown around here is an outgrowth of the system environment being used today and not then. You can always replicate the system environment back then by using a term program connected to your 2SIO and downloading, from within the Term program, the papertape *.bin files.

         
      • mfeberhard
        Well, it *is* a bug... MITS documentation says that switch A8 sets the laoader s stop bits for the 2SIO, but the code actually looks at switch A12 - which the
        Message 3 of 4 , Mar 22 3:56 PM
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          Well, it *is* a bug... MITS documentation says that switch A8 sets the laoader's stop bits for the 2SIO, but the code actually looks at switch A12 - which the documentation says should set the console stop bits.

          For example, If you used a MITS 88-VLCT terminal as your console (which connects to a parallel port) and you used a "MITS" 88-TTY teletype (with a paper tape reader) as your loader, then you would experience this bug - using all MITS hardware from the time of the Altair. And the Teletype loader would not work with the switches set according to the MITS documentation.

          -Martin

          --- In altaircomputerclub@yahoogroups.com, Dan Roganti <ragooman@...> wrote:
          >
          > On Fri, Mar 22, 2013 at 5:58 PM, mfeberhard <eberhard@...> wrote:
          >
          > > **
          > >
          > >
          > > I saw this when I disassembled the loaders some years ago. (My disassebly
          > > of the 3.X and 4.X loaders are in the Files section.) I think this bug
          > > survived because most people either loaded through the console (so the
          > > ports were the same)
          > >
          >
          > such as, a Teletype with a papertape option --the most common console of
          > the day.
          > The term bug being thrown around here is an outgrowth of the system
          > environment being used today and not then. You can always replicate the
          > system environment back then by using a term program connected to your 2SIO
          > and downloading, from within the Term program, the papertape *.bin files.
          >
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