Floppy Disk Controller: Difference between revisions
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More polling mode info, slight reformat, some fixes |
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(using CHS) in Real Mode. The rest of this article deals with creating Protected Mode drivers for the floppy subsystem. |
(using CHS) in Real Mode. The rest of this article deals with creating Protected Mode drivers for the floppy subsystem. |
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Note: the Extended BIOS Int13h functions do not work with floppies. |
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attempting to load your bootloader. So, in the distant future, if the BIOS ever receives 36 more IRQ0 ticks (if you ever return to Real Mode) |
attempting to load your bootloader. So, in the distant future, if the BIOS ever receives 36 more IRQ0 ticks (if you ever return to Real Mode) |
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it may turn off your floppy motors for you, once. |
it may turn off your floppy motors for you, once. |
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Note that code snippets and datasheets name these registers based on their trigrams (e.g. SRA, MSR, DIR, CCR, etc.). |
Note that code snippets and datasheets name these registers based on their trigrams (e.g. SRA, MSR, DIR, CCR, etc.). |
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Use standard "outb" and "inb" commands to access the registers. |
Use standard "outb" and "inb" commands to access the registers. |
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== Reliability == |
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In real hardware, floppy drives are extremely unreliable. On emulators, it doesn't matter -- but for code that is intended for |
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real hardware, make sure to retry every command at least twice more after any error. |
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The basic set of floppy registers can be found in the following enumeration: |
The basic set of floppy registers can be found in the following enumeration: |
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Note2: Emulators will often set the Disk Change flag to "true" after a reset, '''but this does not happen on real hardware''' -- it is |
Note2: Emulators will often set the Disk Change flag to "true" after a reset, '''but this does not happen on real hardware''' -- it is |
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a shared bug in all the emulators that do it. |
a shared bug in all the emulators that do it. Another shared bug is that most emulators do not fire an IRQ6 if disk polling mode is off. |
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Note3: A reset does not change the [[#Configure|drive polling mode or implied seek]] settings. |
Note3: A reset does not change the [[#Configure|drive polling mode or implied seek]] settings. |
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