Altera Embedded Peripherals IP Instrukcja Użytkownika Strona 239

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length Register
The length register specifies the number of bytes to be transferred from the read port to the write port.
The length register is specified in bytes. For example, the value must be a multiple of 4 for word transfers,
and a multiple of 2 for halfword transfers.
The length register is decremented as each data value is written by the write master port. When length
reaches 0 the LEN bit is set. The length register does not decrement below 0.
The length register width is determined at system generation time. It is at least wide enough to span any of
the slave ports mastered by the read or write master ports, and it can be made wider if necessary.
control Register
The control register is composed of individual bits that control the DMA’s internal operation. The control
register’s value can be read at any time. The control register bits determine which, if any, conditions of the
DMA transaction result in the end of a transaction and an interrupt request.
Table 23-5: Control Register Bits
Bit
Number
Bit Name Read/
Write/
Clear
Description
0 BYTE RW Specifies byte transfers.
1 HW RW Specifies halfword (16-bit) transfers.
2 WORD RW Specifies word (32-bit) transfers.
3 GO RW Enables DMA transaction. When the GO bit is set to 0, the
DMA is prevented from executing transfers. When the GO bit
is set to 1 and the length register is non-zero, transfers occur.
4 I_EN RW Enables interrupt requests (IRQ). When the I_EN bit is 1, the
DMA controller generates an IRQ when the status register’s
DONE bit is set to 1. IRQs are disabled when the I_EN bit is 0.
5 REEN RW Ends transaction on read-side end-of-packet. When the
REEN bit is set to 1, a slave port with flow control on the read
side may end the DMA transaction by asserting its end-of-
packet signal.
6 WEEN RW Ends transaction on write-side end-of-packet. When the
WEEN bit is set to 1, a slave port with flow control on the write
side may end the DMA transaction by asserting its end-of-
packet signal.
7 LEEN RW Ends transaction when the length register reaches zero.
When the LEEN bit is 1, the DMA transaction ends when the
length register reaches 0. When this bit is 0, length
reaching 0 does not cause a transaction to end. In this case,
the DMA transaction must be terminated by an end-of-
packet signal from either the read or write master port.
23-8
Register Map
UG-01085
2014.24.07
Altera Corporation
DMA Controller Core
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