Rainbow Electronics DS31256 - Manual (Page 102)

DS31256
102 of 181
Bits 8 to 10/Receive Done-Queue Status-Bit Threshold Setting (RDQT0 to RDQT2). These bits determine
when the DMA sets the receive DMA done-queue write (RDQW) status bit in the status register for DMA
(SDMA) register.
000 = set the RDQW status bit after each descriptor write to the done queue
001 = set the RDQW status bit after 2 or more descriptors are written to the done queue
010 = set the RDQW status bit after 4 or more descriptors are written to the done queue
011 = set the RDQW status bit after 8 or more descriptors are written to the done queue
100 = set the RDQW status bit after 16 or more descriptors are written to the done queue
101 = set the RDQW status bit after 32 or more descriptors are written to the done queue
110 = set the RDQW status bit after 64 or more descriptors are written to the done queue
111 = set the RDQW status bit after 128 or more descriptors are written to the done queue
9.2.5 DMA Channel Configuration RAM
There is a set of 768 dwords (3 dwords per channel times 256 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
000h
004h
008h
HDLC
Channel 1
00Ch
010h
014h
HDLC
Channel 2
BF4h
BF8h
BFCh
HDLC
Channel 256
Fields shown within the thick box
are written by the Host; all other
fields are for usage by the DMA and
can only be read by the Host
Current Descriptor Pointer (16) Start Descriptor Pointer (16)
Byte Count (13)
Threshold
Count (3)
Threshold(3 Unused (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) Unused (4)
CH
EN Size
(2)
Current Descriptor Pointer (16) Start Descriptor Pointer (16)
Byte Count (13)
Threshold
Count (3)
Threshold(3 Unused (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