VRM Region Mode DMA Support
Original Publication Date: 1988-Nov-01
Included in the Prior Art Database: 2005-Feb-15
The Direct Memory Access (DMA) support on the RTPC has two translation modes. The function of the translation mechanism of the hardware is to create the appropriate 32-bit address, relocate within system memory selected memory references by DMA controllers on the I/O channel, and provide the control logic with knowledge of whether the memory reference is directed to system memory or I/O channel attached memory. This translation of addresses is performed under the control of a block of translation control words (TCWs). The TCW mechanism supports two distinct translation modes: page and region. Page mode is used primarily for DMA devices which are usually block structured and transfer data relatively infrequently. The maximum transfer size for page mode devices is 64K-bytes (16-bit devices are limited to 128K-bytes).