
Am79C978A
113
CSR3: Interrupt Masks and Deferral Control
Bit
Name
Description
31-16
RES
Reserved locations. Written as
zeros and read as undefined.
15-13
RES
Reserved locations. Read and
written as zero.
12
MISSM
Missed Frame Mask. If MISSM is
set, the MISS bit will be masked
and unable to set the INTR bit.
This bit is always read/write ac-
cessible. MISSM is cleared by
H_RESET or S_RESET and is
not affected by STOP.
11
MERRM
Memory Error Mask. If MERRM
is set, the MERR bit will be
masked and unable to set the
INTR bit.
This bit is always read/write ac-
cessible. MERRM is cleared by
H_RESET or S_RESET and is
not affected by STOP.
10
RINTM
Receive Interrupt Mask. If RINTM
is set, the RINT bit will be masked
and unable to set the INTR bit.
This bit is always read/write ac-
cessible. RINTM is cleared by
H_RESET or S_RESET and is
not affected by STOP.
9
TINTM
Transmit
TINTM is set, the TINT bit will be
masked and unable to set the
INTR bit.
Interrupt
Mask.
If
This bit is always read/write ac-
cessible. TINTM is cleared by
H_RESET or S_RESET and is
not affected by STOP.
8
IDONM
Initialization
IDONM is set, the IDON bit will be
masked and unable to set the
INTR bit.
Done
Mask.
If
This bit is always read/write ac-
cessible. IDONM is cleared by
H_RESET or S_RESET and is
not affected by STOP.
7
RES
Reserved location. Read and
written as zero.
6
DXSUFLO
Disable Transmit Stop on Under-
flow error.
When DXSUFLO (CSR3, bit 6) is
set to 0, the transmitter is turned
off when an UFLO error occurs
(CSR0, TXON = 0).
When DXSUFLO is set to 1, the
Am79C978A controller graceful-
ly recovers from an UFLO error.
It scans the transmit descriptor
ring until it finds the start of a
new frame and starts a new
transmission.
This bit is always read/write ac-
cessible. DXSUFLO is cleared by
H_RESET or S_RESET and is
not affected by STOP.
5
LAPPEN
Look Ahead Packet Processing
Enable. When set to a 1, the
LAPPEN bit will cause the
Am79C978A controller to gener-
ate an interrupt following the de-
scriptor write operation to the first
buffer of a receive frame. This in-
terrupt will be generated in addi-
tion to the interrupt that is
generated following the descrip-
tor write operation to the last buff-
er of a receive packet. The
interrupt will be signaled through
the RINT bit of CSR0.
Setting LAPPEN to a 1 also en-
ables the Am79C978A control-
ler to read the STP bit of receive
descriptors. The Am79C978A
controller will use the STP infor-
mation to determine where it
should begin writing a receive
packet
’
s data. Note that while in
this mode, the Am79C978A
controller can write intermediate
packet data to buffers whose
descriptors do not contain STP
bits set to 1. Following the write
to the last descriptor used by a
packet, the Am79C978A con-
troller will scan through the next
descriptor entries to locate the
next STP bit that is set to a 1.
The Am79C978A controller will
begin writing the next packets
data to the buffer pointed to by
that descriptor.