Storage Control/Direct Memory Access (Sctljdma) - IBM 3745 Maintenance Information Reference

Storage Control/Direct Memory Access (SCTL/DMA)
The SCTL/DMA main functions are:
1. Allocate main storage access to the different users (CCU/HSB and DMA).
2. Control the different storage operations and ensure data transfer integrity:
• CCU Read/Write
Write requests are buffered in SCTL/DMA so that CCU and storage
operations can overlap ..
• HSB line loading
• DMA burst transfers
Data is aligned and temporarily stored in a buffer so as to optimize the
use of memory bandwidth.
3. Control the HSB operations (line loading). Maintain HSB consistency with
storage during DMA write operations, by means of an HSB line invalidation
mechanism.
4. Check for unauthorized DMA write operations with a DMA storage profect
mechanism.
5. Provide phase signals from a four-phase oscillator to allow CCU/HSB to
generate CCU and SCTL clocks (TCM only).
Chapter 2. Central Control Unit (CCU)
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