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IP2 Chip

addresses are not aligned, so the local bus and the IndustryPack can operate at their maximum data transfer sizes. The FIFO also buffers enough data so that accesses to the local bus are in the burst mode.

Each DMAC also supports command chaining through the use of a singly- linked list built in local (not IP) memory. Each entry in the list includes an IP address, a local bus address, a byte count, a control word, and a pointer to the next entry. When the command chaining mode is enabled, the DMAC reads and executes commands from the list in local memory until all commands are executed.

Each DMAC can be programmed to generate an interrupt request when any specific table entry has completed, when the byte count reaches zero, when an error condition occurs, or when the DMAEND* signal is asserted by the IndustryPack.

The DMA arbiter has two modes of operation. One mode is to implement a round robin type of arbitration, which guarantees equal access to the local bus. The other method is to set the arbitration priority to one of four states. In this case, the priority is constant with one DMA channel having the highest priority, and the other three having the second, third, and fourth highest priority.

Note that the IP specification supports a DMA burst where the DMA cycles can be executed back to back. The DMA arbiter logic will not release a DMA channel until a burst of IP cycles are completed, if the burst protocol is observed. However, if the burst protocol is not observed, the arbiter is released and the next DMA request/grant is resolved. This takes two clock cycles due to the asynchronous clocks controlling the MC68060 local bus and the IP busses. The IP designer should take this into consideration if maximum DMA bandwidth availability is required.

Note also that when the DMA register context is updated for the next command packet, a DMA function is used. The state of the snoop control signals for this DMA function is determined by the settings of jumper J26 (as is the state of the snoop control signals for all other DMA cycle types). Refer to the Hardware Preparation section of your MVME172 installation and use manual.

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Motorola MVME172 manual IP2 Chip