What do you understand by interleaved dma

If a stream ID has been detected in a case where the stream ID add-on flag is invalid, all acknowledge controller validity signals inclusive of the acknowledge controller V validity signal are invalidated, the acknowledge controller V does not output the data prevailing at this time to the processor V , and the stream ID detector validates the acknowledge controller validity signal after the DMA acknowledge signal from the DMA controller is invalidated.

From this point onward, the acknowledge controller V validity signal is held valid until a stream ID other than the video stream ID is detected by the stream ID detector The acknowledge controller V controls the DMA acknowledge signal V and processor V control signal in accordance with the DMA acknowledge signal from the DMA controller so that the data output by the stream ID detector continues being output to the processor V Next, a method of transferring several data streams in memory see FIG.

With reference again to FIG. The stream ID detector in the stream selector distributes the data to the appropriate processor in accordance with the detected stream ID in a manner similar to that described above.

According to the second embodiment of the present invention, a data buffer is provided for each DMA requesting processor in order to perform a data transfer correctly if, in a case where a specific DMA requesting processor is not outputting a DMA request signal, data with respect to this DMA requesting processor has been transferred.

In a case where there are three or more processors for processing data, the number of acknowledge controllers, the number of registers in the stream ID register and the number of data buffers would be the same as the number of processors. In a system of the kind shown in FIG. Accordingly, in the second embodiment of the present invention, the stream ID detector writes data to a data buffer that corresponds to the ID stream currently being selected and, in a case where data is present in the corresponding data buffer, the acknowledge controller outputs the data in this data buffer to the corresponding processor.

However, the stream ID detector writes successively transferred data to the buffer A If the processor A outputs the DMA request signal A in a case where data is present in the buffer A , the acknowledge controller A reads the data out of the buffer A , activates the DMA acknowledge signal A to the processor A and outputs the data.

As a result, it is possible for plural types of data in a single data stream to be distributed to the appropriate data processors.

As a result, not only can interleaved data be distributed but it is also possible to process a plurality of DMA requests with regard to a plurality of data streams the number of which is greater than the number of DMA controller channels. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

All rights reserved. Login Sign up. Search Expert Search Quick Search. DMA transfer of an interleaved stream. United States Patent Wakazu, Yutaka Tokyo, JP. Click for automatic bibliography generation. Download PDF What is claimed is: 1. A system which performs data transfer using direct memory access DMA transfer in response to requests from a plurality of DMA transfer requesting devices, comprising: means for detecting a plurality of stream identifications corresponding to a plurality of different types of data from a data stream in which the plurality of different types of data have been interleaved on a single DMA channel; means for, on the basis of the stream identification that has been detected, separating the data corresponding to the detected stream identification from the data stream; and means for distributing the separated data to the direct memory access transfer requesting device that corresponds to said detected stream identification.

The system according to claim 1, further comprising: means for storing the steam identifications corresponding to the different types of data that have been interleaved in the data stream, in a header position of the data stream; and means for storing one of said stream identifications with each data portion of the data stream. As a rule of thumb, it is best to maximize same-direction contiguoustransfers during moderate system activity. For the most taxing systemflows, however, it is best to select a value in the middle of the rangeto ensure no one peripheral gets locked out of accesses to externalmemory.

This is especially crucial when at least 2 high-bandwidthperipherals like PPIs are used in the system. With this type of arbitration, the first DMAprocess is granted access to the DMA bus for some number of cycles,followed by the second DMA process, and then back to the first. Thechannels alternate in this pattern until all of the data istransferred.

This capability is most useful on dual-core processors for example, when both core processors have tasks that are awaiting adata stream transfer. Without this round-robin feature, the first set of DMA transferswill occur, and the second DMA process will be held off until the firstone completes.

Round-robin prioritization can help insure that bothtransfer streams will complete back-to-back. Of course, this type of scheduling can be performed manually bybuffering data bound for L3 memory in on-chip memory. The processorcore can access on-chip buffers for pre-processing functions with muchlower latency than it can by going off-chip for the same accesses. Thisleads to a direct increase in system performance.

Moreover, bufferingthis data in on-chip memory allows more efficient peripheral DMA accessto this data. For instance, transferring a video frame on-the-fly through a videoport and into L3 memory creates a situation where other peripheralsmight be locked out from accessing the data they need, because thevideo transfer is a high-priority process.

However, by transferringlines incrementally from the video port into L1 or L2 memory, a MemDMAstream can be initiated that will quietly transfer this data into L3 asa low-priority process, allowing system peripherals access to theneeded data. For instance, on Blackfin processors, the core has priorityover DMA accesses, by default, for transactions involving L3 memorythat arrive at the same time.

This means that if a core read from L3occurs at the same time a DMA controller requests a read from L3, thecore will win, and its read will be completed first. Let's look at a scenario that can cause trouble in a real-timesystem. When the processor has priority over the DMA controller onaccesses to a shared resource like L3 memory, it can lock out a DMAchannel that also may be trying to access the memory.

Consider the casewhere the processor executes a tight loop that involves fetching datafrom external memory. DMA activity will be held off until the processor loop hascompleted. It's not only a loop with a read embedded inside that cancause trouble. Activities like cache line fills or nonlinear codeexecution from L3 memory can also cause problems because they canresult in a series of uninterruptible accesses. Another issue meriting consideration is the priority scheme betweenthe processor core s and the DMA controller s.

There is always a temptation to rely on core accesses instead ofDMA at early stages in a project, for a number of reasons. The firstis that this mimics the way data is accessed on a typical prototypesystem. The second is that you don't always want to dig into theinternal workings of the DMA functionality and performance. However,with core and DMA arbitration flexibility, using the memory DMAcontroller to bring data in and out of internal memory gives you morecontrol of your destiny early on in the project.

Six practical uses for DMA inmultimedia systems. Let's consider the case where an active video stream is being broughtinto memory for some type of processing. When the data does not need tobe sent back out for display purposes, it isn't necessary to transferin the blanking data into the buffer in memory.

A processor's video port is often connected directly to a videodecoder or a CMOS sensor and receives samples continuously.

That is,the external device continues to clock in data and blankinginformation. The DMA controller can be set to transfer only the activevideo to memory. Using this type of functionality saves both memoryspace and bus bandwidth. Saving memory is a minorbenefit because extra memory is usually available externally in theform of SDRAM at a small system cost delta.

More important is thebandwidth that is saved in the overall processing period; the timeordinarily used to bring in the blanking data can be re-allocated tosome other task in your system, For example, it can be used to send outthe compressed data or to bring in reference data from past frames. We have previously discussed the need fordouble-buffering as a means of ensuring that current data is notoverwritten by new data until you're ready for this to happen.

Managinga video display buffer serves as a perfect example of this scheme. Normally, in systems involving different rates between source video andthe final displayed content, it's necessary to have a smooth switchoverbetween the old content and the new video frame.

This is accomplished using a double-buffer arrangement. One bufferpoints to the present video frame, which is sent to the display at acertain refresh rate. The second buffer fills with the newest outputframe. When this latter buffer is full, a DMA interrupt signals thatit's time to output the new frame to the display. Prerequisite — Virtual Memory Abstraction is one of the most important aspects of computing. It is a widely implemented Practice in the Computational field.

Memory Interleaving is less or More an Abstraction technique. It is a Technique that divides memory into a number of modules such that Successive words in the address space are placed in the Different modules. Attention reader! Consecutive Word in a Module:. Also, 10, 20, 30…. The DMA command is issued by specifying a pair of a local address and a remote address: for example when a SPE program issues a put DMA command, it specifies an address of its own local memory as the source and a virtual memory address pointing to either the main memory or the local memory of another SPE as the target, together with a block size.

Chat WhatsApp. Cache incoherence due to DMA. Osborne McGraw Hill. ISBN The Art of Electronics Second ed. Cambridge University Press. Microsoft Windows Hardware Development Central. Retrieved Computer bus official and de facto standards wired.

PC Card ExpressCard. Note: interfaces are listed in speed ascending order roughly , the interface at the end of each section should be the fastest Category. From Wikipedia, the free encyclopedia. Online Registration. Regular Lectures. Malang -- Jawa Timur :.

Bandung -- Jawa Barat :. Show all in Bandung Chatting dengan Staf :. Select Language :. Prev Direct inward dialing. Direct navigation Next. Direct memory access Direct memory access DMA is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit CPU. Contents 1 Principle 2 Modes of operation 2.