am79c970 Advanced Micro Devices, am79c970 Datasheet - Page 128

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

28
27
26
25
24
NO_FCS
MORE
ONE
ENP
DEF
STP
(Am7990). This function differs
from the ILACC function for this
bit.
NO_FCS dynamically controls
the generation of FCS on a frame
by frame basis. It is valid only if
the ENP bit is set. When
NO_FCS is set, the state of
DXMTFCS is ignored and trans-
mitter FCS generation is deacti-
vated. When NO_FCS = 0, FCS
generation
DXMTFCS. NO_FCS is set by
the host, and unchanged by the
PCnet-PCI controller. This was a
reserved bit in the LANCE
(Am7990). This function is iden-
tical to the ILACC function for this
bit
MORE indicates that more than
one re-try was needed to trans-
mit a frame. The value of MORE
is written by the PCnet-PCI con-
troller. This bit has meaning only
if the ENP bit is set. ONE, MORE,
and
exclusive.
ONE indicates that exactly one
re-try was needed to transmit a
frame. ONE flag is not valid when
LCOL is set. The value of the
ONE bit is written by the PCnet-
PCI controller. This bit has mean-
ing only if the ENP bit is set.
ONE, MORE, and RTRY are mu-
tually exclusive.
DEFERRED indicates that the
PCnet-PCI controller had to de-
fer while trying to transmit a
frame. This condition occurs if
the channel is busy when the
PCnet-PCI controller is ready to
transmit. DEF is set by the
PCnet-PCI
cleared by the host.
START OF PACKET indicates
that this is the first buffer to be
used by the PCnet-PCI controller
for this frame. It is used for data
chaining buffers. The STP bit
must be set in the first buffer of
the frame, or the PCnet-PCI con-
troller will skip over the descriptor
and poll the next descriptor(s)
until the OWN and STP bits
are set.
STP is set by the host and un-
changed
controller.
END OF PACKET indicates that
this is the last buffer to be used by
RTRY
by
is
controller
the
are
controlled
PCnet-PCI
P R E L I M I N A R Y
mutually
and
Am79C970
by
23–16 RES
15–12 ONES
11–00 BCNT
TMD2
Bit
31
30
BUFF
UFLO
Name
the PCnet-PCI controller for this
frame. It is used for data chaining
buffers. If both STP and ENP are
set, the frame fits into one buffer
and there is no data chaining.
ENP is set by the host and un-
changed
controller.
Reserved locations.
MUST BE ONES. This field is
written by the host and un-
changed
controller.
BUFFER BYTE COUNT is the
usable length of the buffer
pointed to by this descriptor, ex-
pressed as the two’s comple-
ment of the length of the buffer.
This is the number of bytes from
this buffer that will be transmitted
by the PCnet-PCI controller. This
field is written by the host and un-
changed by the PCnet-PCI con-
troller. There are no minimum
buffer size restrictions.
Description
BUFFER ERROR is set by the
PCnet-PCI
transmission when the PCnet-32
controller does not find the ENP
flag in the current buffer and does
not own the next buffer. This can
occur in either of two ways:
1.
2. FIFO underflow occurred
If a Buffer Error occurs, an Un-
derflow Error will also occur.
BUFF is not valid when LCOL or
RTRY error is set during transmit
data chaining. BUFF is set by the
PCnet-PCI
cleared by the host.
UNDERFLOW
cates that the transmitter has
truncated a message due to data
late from memory. UFLO indi-
cates that the FIFO has emptied
before the PCnet-PCI
controller obtained the
STATUS byte
(TMD1[31:24]) of the next
descriptor. BUFF is set by
the PCnet-PCI controller and
cleared by the host. BUFF
error will turn off the trans-
mitter (CSR0, TXON = 0).
The OWN bit of the next
buffer is ZERO.
by
by
controller
controller
the
the
ERROR
PCnet-PCI
PCnet-PCI
AMD
during
1-995
indi-
and