am79c970 Advanced Micro Devices, am79c970 Datasheet - Page 85

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

1
0
Interrupt Line Register (Offset 3Ch)
The Interrupt Line register is an 8-bit register that is used
to communicate the routing of the interrupt. This register
is written by the POST software as it initialized the
PCnet-PCI controller in the system. The register is read
by the network driver to determine the interrupt channel
which the POST software has assigned to the PCnet-
PCI controller. The Interrupt Line register is not modified
by the PCnet-PCI controller. It has no effect on the op-
eration of the device.
The Interrupt Line register is located at offset 3Ch in the
PCI Configuration Space. It is read an written by the
host. It is not effected by H_RESET or S_RESET or as-
serting the SLEEP pin.
Interrupt Pin Register (Offset 3Dh)
This Interrupt Pin register is an 8-bit register indicating
the interrupt pin the PCnet-PCI controller is using. The
value for the PCnet-PCI Interrupt Pin register is 01h,
which corresponds to INTA.
The Interrupt Pin register is located at offset 3Dh in the
PCI Configuration Space. It is read only.
RAP Register
The RAP (Register Address Pointer) register is used to
gain access to CSR and BCR registers on board the
PCnet-PCI controller. The value of the RAP indicates
the address of a CSR or BCR whenever an RDP or BDP
access is performed. That is to say, RAP serves as a
pointer to CSR and BDP space.
As an example of RAP use, consider a read access to
CSR4. In order to access this register, it is necessary to
first load the value 0004h into the RAP by performing a
write access to the RAP offset of 12h (12h when WIO
mode has been selected, 14h when DWIO mode has
been selected). Then a second access is performed
PCnet-PCI controller, this time to the RDP offset of 10h
(for either WIO or DWIO mode). The RDP access is a
read access, and since RAP has just been loaded with
the value of 0004h, the RDP read will yield the contents
of CSR4. A read of the BDP at this time (offset of 16h
when WIO mode has been selected, 1Ch when DWIO
mode has been selected) will yield the contents of
BCR4, since the RAP is used as the pointer into both
BDP and RDP space.
1-952
AMD
IOSPACE
RES
Reserved location. Read as
ZERO, write operations have no
effect.
I/O space indicator. Read as
ONE, write operations have no
effect. Indicating that this Base
Address register describes an
I/O base address.
P R E L I M I N A R Y
Am79C970
RAP: Register Address Port
Bit
31–16 RES
15–8
7–0
Control and Status Registers
The CSR space is accessible by performing accesses to
the RDP (Register Data Port). The particular CSR that is
read or written during an RDP access will depend upon
the current setting of the RAP. RAP serves as a pointer
into the CSR space. RAP also serves as the pointer to
BCR space, which is described in a later section.
CSR0: PCnet-PCI Controller Status Register
Bit
31–16 RES
15
14
BABL
Name
Name
RES
RAP
ERR
Description
Reserved locations. Written as
ZEROs and read as undefined.
Reserved locations. Read and
written as ZEROs.
Register Address Port. The value
of these 8 bits determines which
CSR or BCR will be accessed
when an I/O access to the RDP
or BDP port, respectively, is
performed.
A write access to undefined CSR
or BCR locations may cause un-
expected reprogramming of the
PCnet-PCI control registers. A
read access will yield undefined
values.
RAP is cleared by H_RESET or
S_RESET and is unaffected by
the STOP bit.
Description
Certain bits in CSR0 indicate the
cause of an interrupt. The regis-
ter is designed so that these indi-
cator bits are cleared by writing
ONEs to those bit locations. This
means that the software can read
CSR0 and write back the value
just read to clear the interrupt
condition.
Reserved locations. Written as
ZEROs and read as undefined.
Error is set by the ORing of
BABL, CERR, MISS, and MERR.
ERR remains set as long as any
of the error flags are true. ERR is
read only. Write operations are
ignored.
Babble is a transmitter time-out
error. It indicates that the trans-
mitter has been on the channel