Rainbow Electronics DS3134 - Manual (Page 142)

DS3134
142 of 203
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 18 to 19 / Pending State (PENDST). This field is used by the transmit DMA to keep
track of queued descriptors as they arrive from the Pending Queue and for the DMA to know when it
should create a horizontal linked list of transmit descriptors and where it can find the next valid
descriptor. This field handles standard packets and the PRIST field handles priority packets.
State Next Descriptor Next Pending Descriptor
Pointer field Pointer field
00 not valid not valid
01 valid not valid
10 not valid valid
11 valid valid
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 20 to 21 / Priority State (PRIST). This field is used by the transmit DMA to keep track
of queued priority descriptors as they arrive from the Pending Queue and for the DMA to know when it
should create a horizontal linked list of transmit priority descriptors and where it can find the next valid
priority descriptor. This field handles priority packets and the PENDST field handles standard packets.
State Next Priority Descriptor Next Priority Pending
Pointer field Descriptor Pointer field
00 not valid not valid
01 valid not valid
10 not valid valid
11 valid valid
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 1; Bit 22/ Processing Priority Packet (PPP). This bit will be set to a one when the DMA is
currently processing a priority packet.
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 23 to 31/ Unused. This field is not used by the DMA and could be any value when read
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 0 to 15 / Next Descriptor Pointer. This 16-bit value is the offset from the Transmit
Descriptor Base Address of the next Transmit Packet Descriptor for the packet that is currently being
transmitted. Only valid if EOF = 0 or if EOF = 1 and CV = 1.
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 16 to 31 / Start Descriptor Pointer. This 16-bit value is the offset from the Transmit
Descriptor Base Address of the first Transmit Packet Descriptor for the packet that is currently being
transmitted. If DQS = 0, then this pointer is written back to the Done Queue when the packet has
completed transmission. This field is used by the DMA for processing standard as well as priority
packets.
- FOR DMA USAGE ONLY / HOST CAN ONLY READ THIS FIELD -
dword 3; Bits 0 to 15 / Next Pending Descriptor Pointer. This 16-bit value is the offset from the
Transmit Descriptor Base Address of the first Transmit Packet Descriptor for the packet that is queued up
next for transmission.