GT-96100A Advanced Communication Controller
316
Revision 1.0
13.6
SDMA Descriptor Pointer Registers
Each SDMA channel has three 32-bit registers that reside in a special descriptor’s Dual Port memory located in
the internal address space of the GT-96100A.
Figure 55: SDMA Descriptor Pointer Registers
13.6.1
SDMA Current Receive Descriptor Pointer (SCRDP)
SCRDPx points to the current receive descriptor in memory. The CPU must write this register with the first
descriptor address before enabling the SDMA receive channel. When a SDMA receive channel is enabled it will
fetch the first descriptor pointed to by SCRDPx as part of its SDMA starting procedure.
13.6.2
SDMA Current Transmit Descriptor Pointer (SCTDP)
SCTDPx points to the current transmit descriptor in memory. The CPU must write this register with the first
descriptor address before enabling the SDMA transmit channel. When a SDMA transmit channel is enabled it
will fetch the first descriptor pointed to by SCRDPx as part of its SDMA starting procedure.
13.6.3
SDMA First Transmit Descriptor Pointer (SFTDP)
SFTDPx points to the first descriptor in a transmit frame. The CPU must write this register with the first descrip-
tor address before enabling the SDMA transmit channel. The SDMA transmit controller uses the SFTDP when it
needs to restart a transmission after collision (HDLC mode only). The GT-96100A updates the content of SFTDP
each time it fetches a descriptor with the F (first) bit set to ‘1’.
NOTE: The CPU must write the same value to both SCTDP and SFTDP before enabling the corresponding
SDMA transmit channel.
13.7
Transmit SDMA
13.7.1
Transmit SDMA Definitions
SOF (Start Of Frame descriptor): Descriptor with F (First) bit set to ‘1’.
EOF (End Of Frame descriptor): Descriptor with L (Last) bit set to ‘1’.
F and L bits are set by the CPU before releasing a descriptor to the GT-96100A for transmission.
3
1
3
0
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
1
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
09 8 765 4 3210
SDMAx Current Receive Descriptor Pointer (SCRDPx)
SDMAx First Transmit Descriptor Pointer (SFTDPx)
SDMAx Current Transmit Descriptor Pointer (SCTDPx)