Owner's manual

DS3131
78 of 174
Host Actions
The host typically handles the receive DMA as follows:
1) The host is always trying to make free data buffer space available and therefore tries to fill the free-
queue descriptor.
2) The host either polls, or is interrupted, when some incoming packet data is ready for processing.
3) The host then reads the done-queue descriptor circular queue to find out which channel has data
available, what the status is, and where the receive packet descriptor is located.
4) The host then reads the receive packet descriptor and begins processing the data.
5) The host then reads the next descriptor pointer in the link-listed chain and continues this process
until either a number (from 1 to 7) of descriptors have been processed or an end of packet has been
reached.
6) The host then checks the done-queue descriptor circular queue to see if any more data buffers are
ready for processing.
Figure 9-1. Receive DMA Operation
Free Data Buffer Addres
s
00h
08h
10h
Free Queue Descriptor
s
(circular queue)
00h
04h
08h
Done Queue Descriptors
(circular queue)
Open Descriptor Space
Available for Use by the DMA
Data Buffer Address
Unused
Timestamp CH #2
Status
0Ch
Free Data Buffe
r
(up to 4096 bytes)
Free Data Buffe
r
(up to 4096 bytes)
First Filled
Data Buffe
r
for Channel 2
Free Packet Descriptors & Data Buffers
Used Packet Descriptors & Data Buffers
Single Filled
Data Buffe
r
for Channel 5
Second Filled
Data Buffe
r
for Channel 2
Last Filled
Data Buffe
r
for Channel 2
Single Filled
Data Buffe
r
for Channel 9
unused Free Desc. Ptr.
Free Desc. Ptr.
Free Desc. Ptr.
unused
unused
Free Data Buffer Addres
s
Free Data Buffer Addres
s
Open Descriptor Space
Available for Use by the DMA
# Bytes Next Desc. Ptr.
Data Buffer Address
Timestamp CH #5
Status # Bytes Next Desc. Ptr.
Data Buffer Address
Timestamp CH #2
Status # Bytes Next Desc. Ptr.
Data Buffer Address
Timestamp CH #2
Status # Bytes Next Desc. Ptr.
Data Buffer Address
Timestamp CH #9
Status # Bytes Next Desc. Ptr.
EOF
Status CH #5 Desc. Ptr.
EOF
Status CH #2 Desc. Ptr.
EOF
Status CH #9 Desc. Ptr.
EOF
Status CH
#
Desc. Ptr.