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Advanced Technology Attachment (ATA)
23-2
Freescale Semiconductor
•
One CPU bus for communication with the host processor
•
One DMA bus for communication with the host DMA unit
All internal registers are visible from both busses, allowing smart DMA access to program the interface.
Before accessing the ATA bus, the host must program the timing parameters on the ATA bus. The timing
parameters control the timing on the ATA bus. Most timing parameters are programmable as a number of
clock cycles (1 to 255). Some are implied.
After programming the timing parameters, two protocols can be active at the same time on the ATA bus:
PIO or DMA mode. All transfers between the FIFO and host or DMA busses are zero wait states transfer,
so high speed transfer between FIFO and DMA/host bus is possible.
When a PIO access performed during a running DMA transfer, the DMA transfer pauses, the PIO access
finishes, and the DMA transfer resumes again.
NOTE
The pin multiplexing and control module must be configured to enable the
peripheral function of the appropriate pins (refer to
) prior to configuring the ATA.
23.1.2
Features
The ATA interface has these features:
•
Programmable timing on the ATA bus. Works with wide range of bus frequencies.
•
Compliant with
AT Attachment - 6 with Packet Interface
specification found at
— Supports programmed input/output (PIO) modes 0, 1, 2, 3, and 4
— Supports multiword DMA modes 0, 1, and 2
— Supports ultra DMA modes 0, 1, 2, 3, 4, and 5
•
128-byte FIFO interface
•
FIFO receive alarm, FIFO transmit alarm, and FIFO end of transmission alarm to DMA unit
•
Zero-wait cycles transfer between DMA bus and FIFO allows fast FIFO reading/writing
23.1.3
Modes of Operation
The interface offers two operating modes:
•
PIO Mode
An access to the ATA bus in PIO mode occurs when the host CPU or the host DMA unit reads or
writes ATA PIO register. During PIO transfer the incoming device bus cycle translates to an ATA
PIO bus cycle by the ATA protocol engine. No buffering of data occurs, so the host CPU or host
DMA cycle stalls until the ATA bus read data is available on read or stalls until the device bus data
can be put on the ATA bus during write.
PIO accesses can happen to the bus at any time, even during a running ATA DMA transfer. In this
case, the DMA transfer pauses, the PIO cycle completes, and the DMA transfer resumes.
Содержание MCF54455
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