Contents
Can a DMA be performed between two devices?
DMA transfers can be performed between two devices, between a device and memory, or between memory and memory. This chapter explains transfers between a device and memory only. This chapter provides information on the following subjects: DMA Model Types of Device DMA Managing DMA Resources DMA Software Components: Handles, Windows, and Cookies
Why do we use direct memory access ( DMA )?
Direct memory access (DMA) is used in order to provide high-speed data transfer between peripherals and memory as well as memory to memory. Data can be quickly moved by DMA without any CPU actions. This keeps CPU resources free for other operations.
How does a DMA transfer work on a CPU?
With DMA, the CPU first initiates the transfer, then performs other operations while the transfer is in progress, and finally receives an interrupt from the DMA controller (DMAC) when the operation is complete.
How many channels does a DMA controller have?
The two DMA controllers have 12 channels in total (7 for DMA1 and 5 for DMA2), each dedicated to managing memory access requests from one or more peripherals. It has an arbiter for handling the priority between DMA requests. The DMA controller performs direct memory transfer by sharing the system bus with the Cortex®-M3 core.
How does the DMA controller access the system bus?
In the cycle stealing mode, the DMA controller obtains access to the system bus the same way as in burst mode, using BR (Bus Request) and BG (Bus Grant) signals, which are the two signals controlling the interface between the CPU and the DMA controller.
Which is an example of an I / O port address?
I/O port addresses are ranges of circuits that a device uses to actually send the data after they have gained the CPU’s attention. These are shown in hexadecimal because they are considered to be memory ranges. For example, the keyboard uses the I/O port address 60.
How does direct memory access ( DMA ) work in IA?
To deal with the discontiguous memory, devices for these platforms usually have some kind of scatter-gather DMA capability. Typically, IA systems provide physical addresses for direct memory transfers. On platforms that support DVMA, the system provides the device with a virtual address to perform transfers.