
. . . . .
E X T E R N A L D M A
DMA transfers
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339
External DMA
C
H
A
P
T
E
R
6
T
he external DMA interface provides two external channels for external
peripheral support. Each DMA channel moves data from the source address to the
destination address. These addresses can specify any peripheral on the AHB bus but,
ideally, they specify an external peripheral and external memory.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D M A t r a n s f e r s
DMA transfers can be specified as burst-oriented to maximize AHB bus efficiency.
All transfers are performed in two steps:
1
Data is moved from the source address to a 32-byte buffer in the DMA control
logic.
2
The data is moved from the 32-byte buffer to the destination address.
These two steps are repeated until the DMA transfer is complete.
Note:
Optimal performance is achieved when both the source address and
destination address are aligned.
Initiating DMA
transfers
DMA transfers can be initiated in one of two ways: processor-initiated and external
peripheral initiated.
Processor-
initiated
The processor must do these steps in the order shown:
1
Set up the required buffer descriptors.
2
Configure the DMA Control register for each channel.
3
Write a 1 to both the CE field and the CG field in the DMA Control register for
each channel.
External
peripheral-
initiated
An external peripheral initiates a DMA transfer by asserting the appropriate REQ
signal. Software must have set up the required buffer descriptors as well as the DMA
Control register for each channel, including setting the CE field to 1, before the REQ
signal can be asserted.
Содержание NS9215
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Страница 52: ...P I N O U T 26 5 Power and ground 52 Hardware Reference NS9215...
Страница 80: ...I O C O N T ROL M O D U L E Memory Bus Configuration register 80 Hardware Reference NS9215...
Страница 136: ...WOR KI N G W I TH T H E C P U Noncachable instruction fetches 136 Hardware Reference NS9215...
Страница 202: ...S Y S T E M C O N T RO L M OD U L E RTC Module Control register 202 Hardware Reference NS9215...
Страница 260: ...M E MO R Y C O N T ROL L E R StaticMemory Turn Round Delay 0 3 registers 260 Hardware Reference NS9215...
Страница 354: ...E X T E R N A L D M A DMA Peripheral Chip Select register 354 Hardware Reference NS9215...
Страница 362: ...A E S D AT A E N C R Y P T I O N D E C R Y P T I O N M O D U L E CCM mode 362 Hardware Reference NS9215...
Страница 384: ...I O HU B M OD UL E Module Direct Mode TX Data Last FIFO 384 Hardware Reference NS9215 31 March 2008...
Страница 414: ...S E R I A L C ON T RO L M O D U L E U ART UART Modem Status register 414 Hardware Reference NS9215...
Страница 446: ...S E R I A L C ON T RO L M O D U L E S PI SPI timing characteristics 446 Hardware Reference NS9215...
Страница 472: ...R E A L TI M E C L O C K M O D U L E General Status register 472 Hardware Reference NS9215...
Страница 512: ...TI M I NG Clock timing 512 Hardware Reference NS9215...
Страница 514: ...PA CKA GING Processor Dimensions 514 Hardware Reference NS9215 P r o c e s s o r D i m e n s i o n s...
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Страница 516: ...PA CKA GING Processor Dimensions 516 Hardware Reference NS9215...