am79c970 Advanced Micro Devices, am79c970 Datasheet - Page 41

• Manufacturer Part Number: am79c970
• Description: Pcnettm-pci Single-chip Ethernet Controller For Pci Local Bus
• Manufacturer: Advanced Micro Devices

Figure 17 shows a partial linear burst that occurred while
approaching the transfer of the last bytes of data to a RX
buffer. The linear burst begins when 10 bytes of space
still remain in the RX buffer. (The number of spaces re-
maining for the figure as drawn could be anywhere from
9 to 12. The value of 10-byte spaces has been chosen
just for purposes of illustration.) After the first linear
burst transfer, 6 byte spaces remain. Knowing that the
If a burst cycle is preempted before the last data phase,
the PCnet-PCI controller will finish the current data
phase and release the bus. REQ will stay asserted. The
PCnet-PCI controller will revert to non-burst cycle
1-908
AMD
DEVSEL
FRAME
TRDY
IRDY
C/BE
REQ
GNT
PAR
CLK
AD
1
DEVSEL is sampled by the PCnet-PCI controller.
Figure 17. Partial Linear Burst at the End of Buffer
2
3
0111
n00h
P R E L I M I N A R Y
4
Am79C970
DATA
PAR
5
0000
second transfer will use another 4 bytes of space, the
PCnet-PCI controller is able to predict that the third
transfer will be the last. Therefore, it de-asserts FRAME
on the second transfer to terminate the linear burst op-
eration. However, the PCnet-PCI controller retains own-
ership of the bus so that it may, immediately, make
non-burst transfer(s) to the last two spaces in the buffer.
accesses following the preemption event. In this case,
linear bursting will next occur when the memory address
being accessed next meets the linear burst starting ad-
dress requirements.
DATA
PAR
6
PAR
7
0111
n08h
8
DATA
1100
PAR
9
PAR
10
18220C-19