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ATA PIO Mode: Difference between revisions
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According to the ATA specs, PIO mode must always be supported by all ATA-compliant drives as the default data transfer mechanism.
PIO mode uses a tremendous amount of CPU resources
However, when a computer is just beginning to boot, there are no other processes. So PIO mode is an excellent and simple interface to utilize during bootup
Please note that this article deals with what are now styled PATA hard disks, as opposed to SATA hard disks.
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==Master/Slave Drives==
There is only one wire dedicated to selecting which drive on each bus is active. It is either electrically "high" or "low", which means that there can never be more than two devices operational on any ATA bus. They are called the master and the slave devices, for no particular reason.
==Primary/Secondary Bus==
Current disk controller chips almost always support two ATA buses per chip. There is a standardized set of IO ports to control the disks on the buses. The first two buses are called the Primary and Secondary ATA bus, and are almost always controlled by IO ports 0x1F0 through 0x1F7, and 0x170 through 0x177, respectively (unless you change it). The associated Device Control Registers/Alternate Status ports are IO ports 0x3F6, and 0x376, respectively. The standard IRQ for the Primary bus is IRQ14
If the next two buses exist, they are normally controlled by IO ports 0x1E8 through 0x1EF, and 0x168 through 0x16F, respectively. The associated Device Control Registers/Alternate Status ports are IO ports 0x3E6, and 0x366.
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(Using a Software Reset -- adapted from PypeClicker)
<
/* on Primary bus: ctrl->base =0x1F0, ctrl->dev_ctl =0x3F6. REG_CYL_LO=4, REG_CYL_HI=5, REG_DEVSEL=6 */
int detect_devtype (int slavebit, struct DEVICE *ctrl)
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return ATADEV_UNKNOWN;
}
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(Note: the following routines should all include some form of OS-specific timeout.)
<
; do a singletasking PIO ATA read
; inputs: ebx = # of sectors to read, edi -> dest buffer, esi -> driverdata struct, ebp = 4b LBA
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pop eax
ret
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* http://www.ata-atapi.com -- Public Domain C driver sourcecode, including SATA, Busmatering DMA, ATAPI -- not perfect, but good.
* [http://hddguru.com/content/en/documentation/ HDD Guru] -- The actual ATA specs from the first one that was released in 1994 to the 8th one in 2006.
* An
* [http://www.fysnet.net/media_storage_devices.htm A book] written by somebody on the forum about ATA and SATA.
* [https://github.com/omarrx024/xos/blob/master/kernel/blkdev/ata.asm ATA PIO driver in assembly.]
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