223cc6685e
git-svn-id: svn://svn.compuextreme.de/Viitor/V963/Viitor_cc65@5933 504e572c-2e33-0410-9681-be2bf7408885
50 lines
1.8 KiB
HTML
50 lines
1.8 KiB
HTML
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<TITLE>Commodore 610 specific information for cc65: Limitations</TITLE>
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<H2><A NAME="limitations"></A> <A NAME="s6">6.</A> <A HREF="cbm610.html#toc6">Limitations</A></H2>
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<H2><A NAME="ss6.1">6.1</A> <A HREF="cbm610.html#toc6.1">Kernal and hardware access</A>
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</H2>
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<P>Since the program runs in bank 1, and the kernal and all I/O chips are located
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in bank 15, calling ROM routines or accessing hardware needs special code. The
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cc65 runtime implements wrappers for all functions in the kernal jump table.
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While this simplifies things, it should be noted that the wrappers do have
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quite an impact on performance: A cross bank call has an extra 300µs
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penalty added by the wrapper.</P>
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<H2><A NAME="ss6.2">6.2</A> <A HREF="cbm610.html#toc6.2">Interrupts</A>
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</H2>
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<P>Compiled programs contain an interrupt handler that runs in the program bank.
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This has several advantages, one of them being performance (see cross bank
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call overhead mentioned above). However, this introduces one problem:
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Interrupts are lost while the CPU executes code in the kernal bank. As a
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result, the clock may go wrong and (worse) serial interrupts may get lost.</P>
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<P>Since the cc65 runtime does only call the kernal for disk I/O, this means that
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a program should not do file I/O while it depends on interrupts.</P>
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