Altera cyclone V Technical Reference page 1256

cv_5v4
2016.10.28
Bit
14 RCH: Second Address Chained
When set, this bit indicates that the second address in the descriptor is the next descriptor
address rather than the second buffer address. When this bit is set, RBS2 (RDES1[28:16]) is a
"don't care" value. RDES1[15] takes precedence over RDES1[14].
13 Reserved
12:0 RBS1: Receive Buffer 1 Size
Indicates the first data buffer size in bytes. The buffer size must be a multiple of 4, even if the
value of RDES2 (buffer1 address pointer), in the Receive Descriptor Field 2 (RDES2), is not
aligned. When the buffer size is not a multiple of 4, the resulting behavior is undefined. If this
field is 0, the DMA ignores this buffer and uses Buffer 2 or the next descriptor depending on
the value of RCH (Bit 14). For more information about calculating buffer sizes, refer to the
Buffer Size Calculations section in this chapter.
Related Information
Buffer Size Calculations
•
• Receive Descriptor Field 2 (RDES2)
• Receive Descriptor Field 3 (RDES3)
Receive Descriptor Fields (RDES2) and (RDES3)
Receive Descriptor Field 2 (RDES2)
Table 17-13: Receive Descriptor Field 2 (RDES2)
Bit
31:0
Related Information
Host Data Buffer Alignment
Ethernet Media Access Controller
Send Feedback
†
on page 17-19
Buffer 1 Address Pointer
These bits indicate the physical address of Buffer 1. There are no limitations on the buffer
address alignment except for the following condition: The DMA uses the value
programmed in RDES2[1:0] for its address generation when the RDES2 value is used to
store the start of the frame. The DMA performs a write operation with the RDES2[1:0]
bits as 0 during the transfer of the start of the frame but the frame is shifted as per the
actual buffer address pointer. The DMA ignores RDES2[1:0] if the address pointer is to a
buffer where the middle or last part of the frame is stored. For more information about
buffer address alignment, refer to the Host Data Buffer Alignment section.
on page 17-18
Receive Descriptor Fields (RDES2) and (RDES3)
Description
on page 17-41
on page 17-42
Description
†
Altera Corporation
17-41