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Floppy Disk Controller: Difference between revisions
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Added LBA to CHS and vice versa equations
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numbers are typically 0 to 79 inclusive, heads are 0 or 1, and sector numbers are 1 to 18 inclusive. Asking for sector number 0
is always highly illegal and this is a major source of errors in prototype driver code.
It is, however, much more logical to address things in LBA (Logical Block Addressing), as the first sector is at 0 (like an array).
Conversion between the two is rather simple. The equations are as follows:
''CYL = LBA / (HPC * SPT)''
''HEAD = (LBA % (HPC * SPT)) / SPT''
''SECT = (LBA % (HPC * SPT)) % SPT + 1''
''LBA = ( ( CYL * HPC + HEAD ) * SPT ) + SECT - 1''
This can be described in C with the following code:
<source lang="c">
void lba_2_chs(uint32_t lba, uint16_t* cyl, uint16_t* head, uint16_t* sector)
{
*cyl = lba / (2 * FLOPPY_144_SECTORS_PER_TRACK);
*head = ((lba % (2 * FLOPPY_144_SECTORS_PER_TRACK)) / FLOPPY_144_SECTORS_PER_TRACK);
*sector = ((lba % (2 * FLOPPY_144_SECTORS_PER_TRACK)) % FLOPPY_144_SECTORS_PER_TRACK + 1);
}
</source>
You would then send this data to the floppy controller.
=== DMA Data Transfers ===
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