Rainbow Electronics DS3134 - Manual (Page 117)

DS3134
117 of 203
RECEIVE DMA CONFIGURATION RAM Figure 8.1.5A
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 0; Bits 0 to 31 / Current Data Buffer Address. The current 32-bit address of the data buffer that
is being used. This address is used by the DMA to keep track of where data should be written to as it
comes in from the Receive FIFO.
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 0 to 15 / Current Descriptor Pointer. This 16-bit value is the offset from the Receive
Descriptor Base Address of the current Receive Descriptor being used by the DMA to describe the
specifics of the data being stored in the associated data buffer.
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 16 to 31 / Starting Descriptor Pointer. This 16-bit value is the offset from the Receive
Descriptor Base Address of the first Receive Descriptor in a link-list chain of descriptors. This pointer
will be written into the Done Queue by the DMA after a specified number of data buffers (see the
Threshold value below) have been filled.
- HOST MUST CONFIGURE -
dword 2; Bit 0 / Channel Enable (CHEN). This bit is controlled by the host to enable and disable a
HDLC channel.
0 = HDLC Channel Disabled
1 = HDLC Channel Enabled
dmarcram
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) 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