AMD SC2200 UltraDMA/33 Signal Definitions, UltraDMA/33 Mode, Stop, DMARDY# Strobe Ideiordy, 154

32580B Core Logic Module

6.2.3.4UltraDMA/33 Mode

The IDE controller of the Core Logic module supports UltraDMA/33. It utilizes the standard IDE Bus Master func- tionality to interface, initiate and control the transfer. UltraDMA/33 definition also incorporates a Cyclic Redun- dancy Checking (CRC) error checking protocol to detect errors.

The UltraDMA/33 protocol requires no extra signal pins on the IDE connector. The IDE controller redefines three stan- dard IDE control signals when in UltraDMA/33 mode. These definitions are shown in Table 6-2.

Table 6-2. UltraDMA/33 Signal Definitions

IDE Controller	UltraDMA/33	UltraDMA/33
Channel Signal	Read Cycle	Write Cycle
IDE_IOW#	STOP	STOP
IDE_IOR#	DMARDY#	STROBE
IDE_IORDY	STROBE	DMARDY#

All other signals on the IDE connector retain their func- tional definitions during the UltraDMA/33 operation.

IDE_IOW# is defined as STOP for both read and write transfers to request to stop a transaction.

IDE_IOR# is redefined as DMARDY# for transferring data from the IDE device to the IDE controller. It is used by the IDE controller to signal when it is ready to transfer data and to add wait states to the current transaction. IDE_IOR# sig- nal is defined as STROBE for transferring data from the IDE controller to the IDE device. It is the data strobe signal driven by the IDE controller on which data is transferred during each rising and falling edge transition.

IDE_IORDY is redefined as STROBE for transferring data from the IDE device to the IDE controller during a read cycle. It is the data strobe signal driven by the IDE device on which data is transferred during each rising and falling edge transition. IDE_IORDY is defined as DMARDY# dur- ing a write cycle for transferring data from the IDE control- ler to the IDE device. It is used by the IDE device to signal when it is ready to transfer data and to add wait states to the current transaction.

UltraDMA/33 data transfer consists of three phases, a star- tup phase, a data transfer phase and a burst termination phase.

The IDE device begins the startup phase by asserting IDE_DREQ. When ready to begin the transfer, the IDE con- troller asserts IDE_DACK#. When IDE_DACK# is asserted, the IDE controller drives IDE_CS0# and IDE_CS1# asserted, and IDE_ADDR[2:0] low. For write cycles, the IDE controller negates STOP, waits for the IDE device to assert DMARDY#, and then drives the first data WORD and STROBE signal. For read cycles, the IDE controller negates STOP, and asserts DMARDY#. The IDE device then sends the first data WORD and asserts STROBE.

The data transfer phase continues the burst transfers with the Core Logic and the IDE via providing data, toggling STROBE and DMARDY#. The IDE_DATA[15:0] is latched by receiver on each rising and falling edge of STROBE. The transmitter can pause the burst cycle by holding STROBE high or low, and resume the burst cycle by again toggling STROBE. The receiver can pause the burst cycle by negating DMARDY# and resumes the burst cycle by asserting DMARDY#.

The current burst cycle can be terminated by either the transmitter or the receiver. A burst cycle must first be paused as described above before it can be terminated. The IDE controller can then stop the burst cycle by assert- ing STOP, with the IDE device acknowledging by negating IDE_DREQ. The IDE device then stops the burst cycle by negating IDE_DREQ and the IDE controller acknowledges by asserting STOP. The transmitter then drives the STROBE signal to a high level. The IDE controller then puts the result of the CRC calculation onto the IDE_DATA[15:0] while de-asserting IDE_DACK#. The IDE device latches the CRC value on the rising edge of IDE_DACK#.

The CRC value is used for error checking on UltraDMA/33 transfers. The CRC value is calculated for all data by both the IDE controller and the IDE device during the UltraDMA/33 burst transfer cycles. This result of the CRC calculation is defined as all data transferred with a valid STROBE edge while IDE_DACK# is asserted. At the end of the burst transfer, the IDE controller drives the result of the CRC calculation onto IDE_DATA[15:0] which is then strobed by the de-assertion of IDE_DACK#. The IDE device compares the CRC result of the IDE controller to its own and reports an error if there is a mismatch.

The timings for UltraDMA/33 are programmed into the DMA control registers:

•Channel 0 Drive 0 DMA Control Register (F2 Index 44h)

•Channel 0 Drive 1 DMA Control Register (F2 Index 4Ch)

•Channel 1 Drive 0 DMA Control Register (F2 Index 54h)

•Channel 1 Drive 1 DMA Control Register (F2 Index 5Ch)

The bit formats for these registers are described in Table 6- 35 on page 266. Note that F2 Index 44h[20] is used to select either Multiword or UltraDMA mode. Bit 20 = 0 selects Multiword DMA mode. If bit 20 = 1, then UltraDMA/33 mode is selected. Once mode selection is made using this bit, the remaining DMA Control registers also operate in the selected mode.

Also listed in the bit formats are recommended values for both Multiword DMA Modes 0-2 and UltraDMA/33 Modes 0-2. Note that these are only recommended settings and are not 100% tested.

154 AMD Geode™ SC2200 Processor Data Book