Rainbow Electronics DS3134 - Manual (Page 140)

DS3134
140 of 203
Bits 8 to 10 / Transmit Done Queue Status Bit Threshold Setting (TDQT0 to TDQT2). These 3 bits
determine when the DMA will set the Transmit DMA Done Queue Write (TDQW) status bit in the Status
Register for DMA (SDMA) register.
000 = set the TDQW status bit after each descriptor write to the Done Queue
001 = set the TDQW status bit after 2 or more descriptors are written to the Done Queue
010 = set the TDQW status bit after 4 or more descriptors are written to the Done Queue
011 = set the TDQW status bit after 8 or more descriptors are written to the Done Queue
100 = set the TDQW status bit after 16 or more descriptors are written to the Done Queue
101 = set the TDQW status bit after 32 or more descriptors are written to the Done Queue
110 = set the TDQW status bit after 64 or more descriptors are written to the Done Queue
111 = set the TDQW status bit after 128 or more descriptors are written to the Done Queue
8.2.5 DMA CHANNEL CONFIGURATION RAM
Onboard the device there is a set of 1536 dwords (6 dwords per channel times 256 channels) that are used
by the Host to configure the DMA and by the DMA to store values locally when it is processing a packet.
Most of the fields within the DMA Configuration RAM are for use by the DMA and the Host will never
write to these fields. The Host is only allowed to write (i.e. configure) to the lower word of dword 1 for
each HDLC channel. The Host configurable fields are denoted with a thick box as shown below.
Transmit DMA Configuration RAM Figure 8.2.5A
dmatcram
msb
31 lsb
0
Transmit DMA Configuration RAM
000h
004h
008h
HDLC
Channel
1
00Ch
010h
014h
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
Next Descriptor Pointer (16)
Next Priority Pending Descriptor Pointer (16)
Byte Count (13)
Current Packet Data Buffer Address (32)
Start Descriptor Pointer (16)
CH
EN
Last Pending Descriptor Pointer (16) Next Pending Descriptor Pointer (16)
Next Priority Descriptor Pointer (16)
Last Priority Pending Descriptor Pointer (16)
DQS
unused (16)
EOF CV
PEND
ST(2) PRI
ST(2)
unused (9)
17D8h
17DCh
17F0h
17F4h
17F8h
17FCh
PPP
un-
used
Next Descriptor Pointer (16)
Next Priority Pending Descriptor Pointer (16)
Byte Count (13)
Current Packet Data Buffer Address (32)
Start Descriptor Pointer (16)
CH
EN
Last Pending Descriptor Pointer (16) Next Pending Descriptor Pointer (16)
Next Priority Descriptor Pointer (16)
Last Priority Pending Descriptor Pointer (16)
DQS
unused (16)
EOF CV
PEND
ST(2) PRI
ST(2)
unused (9) PPP
un-
used