Table 102: Unaligned Buffer Format Dma Descriptor First Doubleword; Table 103: Unaligned Buffer Format Dma Descriptor Second Doubleword - Broadcom BCM1250 User Manual

BCM1250/BCM1125/BCM1125H

Table 102: Unaligned Buffer Format DMA Descriptor First Doubleword

Bits Name
39:0 addr The base address of the data buffer.
47:40 unused Unused. If extra_status is enabled the receive DMA engine will overwrite this field.
48 reserved Reserved.
49 interrupt If this bit is set an interrupt will be raised when the DMA engine has finished using this descriptor.
50 reserved Reserved.
63:51 status In the first descriptor of a received packet this field will be updated with the packet status at the end
of reception. The flags are described in
MACs" on page

Table 103: Unaligned Buffer Format DMA Descriptor Second Doubleword

Bits Name
3:0 options
7:4 reserved
21:8 size
47:22 reserved
49:48 pkt_size_msb
63:50 pkt_size
Page 170 Section 7: DMA
171.
This field sets the per packet options that are sent to the interface. The options depend on the
channel, and are outlined below.
Reserved.
This field specifies the buffer size in bytes. This field must be set to the number of bytes of data
in the buffer plus bits [4:0] of the start address in the dscr_a addr field.
The DMA engine behavior is UNPREDICTABLE if this size is set to be less than the value of bits
[4:0] of the address in dscr_a.
Reserved.
This field provides bits [15:14] of the packet size. (Note that if packets greater than 16K-1 are
used only the low 14 bits of the length is added to the RMON counters.)
In the first descriptor of a packet this field contains the packet length. In a transmit channel the
length is written by the CPU as part of setting up the descriptor and is passed to the interface. In
a receive channel the length is written back into the descriptor at the end of reception. In unaligned
buffer mode this field is extended to 16 bits using the pkt_size_msb field as the upper two bits.
B r oadco m C orp or ati on
dscr_a
Description
Section: "Option and Flag Bits for Ethernet
dscr_b
Description
User Manual
10/21/02
Document 1250_1125-UM100CB-R