ATA PIO Mode: Difference between revisions
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→See Also: the tutorial from the forum was added to the wiki in the 'PCI IDE Controller' article |
m made the udma formula better |
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2According to the ATA specs, PIO mode must always be supported by all ATA-compliant drives as the default data transfer mechanism. |
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PIO mode uses a tremendous amount of CPU resources, because every byte of data transferred between the disk and the CPU must be sent through the CPU's [[Inline Assembly/Examples#I\O access|IO port bus]] (not the memory). On some CPUs, PIO mode can still achieve actual transfer speeds of 16MB per sec, but no other processes on the machine will get any CPU time. |
PIO mode uses a tremendous amount of CPU resources, because every byte of data transferred between the disk and the CPU must be sent through the CPU's [[Inline Assembly/Examples#I\O access|IO port bus]] (not the memory). On some CPUs, PIO mode can still achieve actual transfer speeds of 16MB per sec, but no other processes on the machine will get any CPU time. |
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* uint16_t 83: Bit 10 is set if the drive supports LBA48 mode. |
* uint16_t 83: Bit 10 is set if the drive supports LBA48 mode. |
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* uint16_t 88: The bits in the low byte tell you the supported UDMA modes, the upper byte tells you which UDMA mode is active. If the active mode is not the highest supported mode, you may want to figure out why. ''Notes: The returned uint16_t should look like this in binary: 0000001 00000001. Each bit corresponds to a single mode. E.g. if the decimal number is 257, that means that only UDMA mode 1 is supported and running (the binary number above) if the binary number is 515, the binary looks like this, 00000010 00000011, that means that UDMA modes 1 and 2 are supported, and 2 is running. This is true for every mode. If it does not look like that, e.g 00000001 00000011, as stated above, you may want to find out why. The formula for finding out the decimal number is |
* uint16_t 88: The bits in the low byte tell you the supported UDMA modes, the upper byte tells you which UDMA mode is active. If the active mode is not the highest supported mode, you may want to figure out why. ''Notes: The returned uint16_t should look like this in binary: 0000001 00000001. Each bit corresponds to a single mode. E.g. if the decimal number is 257, that means that only UDMA mode 1 is supported and running (the binary number above) if the binary number is 515, the binary looks like this, 00000010 00000011, that means that UDMA modes 1 and 2 are supported, and 2 is running. This is true for every mode. If it does not look like that, e.g 00000001 00000011, as stated above, you may want to find out why. The formula for finding out the decimal number is 257 * 2^POSITION + 1. note that you do not add the one if POSITION is zero.'' |
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* uint16_t 93 from a master drive on the bus: Bit 11 is supposed to be set if the drive detects an 80 conductor cable. ''Notes: if the bit is set then 80 conductor cable is present and UDMA modes > 2 can be used; if bit is clear then there may or may not be an 80 conductor cable and UDMA modes > 2 shouldn't be used but might work fine. Because this bit is "master device only", if there is a slave device and no master there is no way information about cable type (and would have to assume UDMA modes > 2 can't be used).'' |
* uint16_t 93 from a master drive on the bus: Bit 11 is supposed to be set if the drive detects an 80 conductor cable. ''Notes: if the bit is set then 80 conductor cable is present and UDMA modes > 2 can be used; if bit is clear then there may or may not be an 80 conductor cable and UDMA modes > 2 shouldn't be used but might work fine. Because this bit is "master device only", if there is a slave device and no master there is no way information about cable type (and would have to assume UDMA modes > 2 can't be used).'' |
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