Browse Prior Art Database

SCANNING DMA CONTROLLER FOR MICROPROCESSOR AND DSP DEVICES

IP.com Disclosure Number: IPCOM000008542D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-21
Document File: 2 page(s) / 119K

Publishing Venue

Motorola

Related People

Kevin Patrick Godfrey: AUTHOR

Abstract

A Scanning Direct Memory Access controller reduced using the proposed Scanning DMA is proposed which can react in a data dependant Controller which has a mechanism to detect the manner to save software overhead of searching block delimiter, close the current buffer and start through data buffers for data structure and control tilling a new buffer. A processor interrupt can occur characters. The key to the Scanning DMA when the block delimiter is detected. Software now Controller is to scan the data as it is being moved handles data on a block basis where all data in each by the DMA controller. block relates to the same message or task.

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MOIOROLA Technical Developments

SCANNING DMA CONTROLLER FOR MICROPROCESSOR AND DSP DEVICES

by Kevin Patrick Godfrey

  A Scanning Direct Memory Access controller reduced using the proposed Scanning DMA is proposed which can react in a data dependant Controller which has a mechanism to detect the manner to save software overhead of searching block delimiter, close the current buffer and start through data buffers for data structure and control tilling a new buffer. A processor interrupt can occur characters. The key to the Scanning DMA when the block delimiter is detected. Software now Controller is to scan the data as it is being moved handles data on a block basis where all data in each by the DMA controller. block relates to the same message or task.

  There are many applications for a Scanning DMA Controller, especially in conjunction with RISC microprocessors and DSPs which are opti- mised to run loops from an instruction cache. The overhead associated context switching, change of flow by branching and off-chip memory accesses during a software data searching procedure, reduce processor throughput considerably.

DATA DEPENDANT SCANNING DMA

  The Scanning DMA Controller performs a data check during every data movement. When data is found that matches a programmable register, the Scanning DMA Controller generates an interrupt and advances to the next data buffer. The data scan- ning occurs while data is present on the processor's data bus during the read/write cycles using a com- parator of the same width as the data bus. A mask register allows detection of a delimiter less than the width of the data bus.

CURRENT DMA CONTROLLER MECHANISMS.

Conventionally there are two ways to stop a DMA controller and move to the next data buffer:

* the DMA controller counts data moves and has determined that the current data buffer is full, or

  With the Scanning DMA Controller, the user now has three mechanisms to stop data transfer and move to the next data buffer: the hardware signal and data counters as described earlier and the new data scanner.


* a hardware signal indicates that the peripheral or
device sourcing data has determined that a new
buffer should begin.

  Often the data being moved has a block struc- ture with varying block lengths and defined block delimiters, but the DMA controller cannot react to this structure. Using a conventional DMA controller connected to an incoming data stream, the processor must subsequently perform a software search for the block delimiters and structure, then act accord- ingly when one is found. The change of flow creates additional load when software first detects the block delimiter and then reacts.

This additional processor activity can be

  The comparator...