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3.13 Direct memory access controller (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.

The DMA controller has up to 6 channels in total, each dedicated to managing memory access

requests from one or more peripherals. It has an arbiter for handling the priority between DMA

requests. For more details, refer to “PrimeCell® μDMA Controller (PL230)” from the Technical

Reference Manual

•

6 channels

•

Each channel is connected to dedicated hardware DMA requests and software trigger is

also supported on each channel.

•

Priorities between requests from the DMA channels are software programmable (2 levels

consisting of high, default)

•

Memory-to-memory transfer (software request only)

•

TCP/IP-to-memory transfer (software request only)

•

SPI/UART-to-memory transfer (hardware request and software request)

•

Access to Flash, SRAM, APB and AHB peripherals as source and destination

DMA request mapping

The hardware requests from the peripherals (UART0, UART1, SSP0, SSP1) are simply connected

to the DMA. Refer to Table 5 which lists the DMA requests for each channel.

Table 5 Summary of the DMA requests for each channel

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Hardware

Request

SSP0_TX

SSP0_RX

SSP1_TX

SSP1_RX

UART0_TX

UART0_RX

UART1_TX

UART1_RX

NONE

Software

Request(1)

Support

Software request is the only way to use DMA for memory-to-memory or TCP/IP-to-memory.

3.14 Timers and watchdogs

3.14.1

System tick timer

System tick timer(SysTick) is part of the ARM Cortex-M0 core



Simple 24bit timer.



Clocked internally by the system clock or the system clock/2.

The SysTick timer is an integral part of Cortex-M0. The SysTick timer is intended to generated

a fixed 10 millisecond interrupt for use by an operating system or other system management

software.

Since the SysTick timer is a part of the Cortex-M0, it facilitates porting of software by

providing a standard timer that is available on Cortex-M0 based devices.

The SysTick timer can be used for :



An RTOS tick timer which fires at a programmable rate (for example 100 Hz) and

invokes a SysTick routine.



A high-speed alarm timer using the core clock.



A simple counter. Software can use this to measure time to completion and time used.

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