Rainbow Electronics DS3131 - Manual (Page 93)

DS3131
93 of 174
9.2.5 DMA Configuration RAM
There is a set of 120 dwords (3 dwords per channel times 40 channels) on-board the device that the host
uses to configure the DMA. It uses the DMA to store values locally when it is processing a packet. Most
of the fields within the DMA configuration RAM are for DMA use and the host never writes to these
fields. The host is only allowed to write (configure) to the lower word of dword 2 for each HDLC
channel. The host-configurable fields are denoted with a thick box as shown below.
Figure 9-9. Receive DMA Configuration RAM
MSB
31
LSB
0
Receive DMA Configuration RAM
Fields shown within the thick box are written by
the host. All other fields are for DMA usage and
can only be read by the host.
Current Descriptor Pointer (16) Start Descriptor Pointer (16)
Byte Count (13)
Threshold
Count (3)
Threshold(3) Offset (4)
CH
EN Size
(2)
Current Descriptor Pointer (16)
Current Packet Data Buffer Address (32)
Start Descriptor Pointer (16)
Byte Count (13)
Threshold
Count (3)
Threshold(3) Offset (4)
CH
EN Size
(2)
Current Descriptor Pointer (16) Start Descriptor Pointer (16)
Byte Count (13)
Threshold
Count (3)
Threshold(3) Offset (4)
CH
EN Size
(2)
Current Packet Data Buffer Address (32)
Current Packet Data Buffer Address (32)
unused (5) FBF
unused (5) FBF
unused (5) FBF
dword 0
dword 1
dword 2
HDLC
CH 2
dword 0
dword 1
dword 2
HDLC
CH 1
dword 0
dword 1
dword 2
HDLC
CH 40