
. . . . .
I / O H U B M O D U L E
DMA controller
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365
Buffer descriptors
The peripheral buffer data is held in buffers in external memory, linked together
using buffer descriptors. The buffer descriptors are 16 bytes in length and are
located contiguously in external memory.
This is the format of the buffer descriptor:
Source address
[pointer]
The source address pointer points to the start of the buffer in system memory.
For transmit channels, the address can start on any byte boundary.
For receive channels, the address must be a 32-bit word aligned.
Buffer length
The buffer length is the length of the buffer in bytes, and allows a buffer size of up to
64k–1 bytes to be in a single buffer. Bits 31:16 are not used.
For receive channels, the buffer length field is updated with the actual number of
bytes written to memory, as the peripheral has the ability to close the buffer early.
Control[15] – W
The Wrap (W) bit, when set, tells the DMA controller that this is the last buffer
descriptor within the continuous list of descriptors. The next descriptor is found using
the initial DMA channel buffer descriptor pointer. When the W bit is not set, the next
buffer descriptor is found using the 16-byte offset.
Control[14] – I
The Interrupt (I) bit, when set, tells the DMA controller to issue an interrupt when the
buffer is closed due to normal channel completion.
Control[13] – L
This is the Last (L) bit.
For transmit channels, firmware sets the L bit when the current buffer is the
last in the packet.
For receive channels. hardware sets the L bit when the current buffer is closed
by status bits received from the peripheral device. Status bits can include
conditions such as a character gap timeout, character match, or error
condition.
Control[12] – F
This is the Full (F) bit.
Address
Description
0
Source address
4
Reserved
Buffer length
8
Reserved
C
Control
Status
Содержание NS9215
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Страница 44: ...P I N O U T 26 5 System clock 44 Hardware Reference NS9215 System clock drawing...
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...