CN8478 Datasheet, PDF (117/221 Pages) Conexant Systems, Inc – Multichannel Synchronous Communications Controller (MUSYCC)

CN8478/CN8474A/CN8472A/CN8471A
Multichannel Synchronous Communications Controller (MUSYCC™)
5.0 Memory Organization
5.2 Descriptors
5.2.4.2 Note for
Interrupt Driven Drivers
5.2.4.3 Head Pointer
An interrupt from MUSYCC does not imply that MUSYCC read a buffer status
descriptor and made it host-owned.
As mentioned in Note (2) in Table 5-31, the occurrence of a MUSYCC
interrupt and a buffer status descriptor update are not time correlated. The delay
of the buffer status descriptor update is a maximum of 2 HDLC frames after the
interrupt.
The driver must read the owner field to confirm its ownership before writing a
new buffer status descriptor. If the driver receives an interrupt and does not detect
a host-owned buffer, it should wait a minimum of 2 HDLC frames before
signaling an abnormal condition.
The requirement to check the buffer status descriptor is applicable only when
buffer status descriptor updates are enabled (INHRBSD = 0).
The head pointer points to the first message descriptor in a list of descriptors
assigned to a channel’s transmitter or receiver.
A head pointer allows the host to specify a new list of descriptors to use for
channel processing. This mechanism can be used after a reset to kick-start or
reactivate channel processing which has completely processed the current list of
descriptors.
A head pointer also allows the host to generate a new list of descriptors in
memory before performing a list transition; that is, while MUSYCC processes
data in one list, the host can process data in a separate list, and, when appropriate,
can switch the lists.
Table 5-20 lists the head pointers and their descriptions.
Table 5-20. Head Pointer
Bit
Field
Name
31:2
HEADPTR[29:0]
1:0
HEADPTR[1:0]
Value
0
Description
These 30 bits are appended with 00b to form a dword-aligned 32-bit address. This
address points to the first Message Descriptor in a list of descriptors.
Ensures dword alignment.
5.2.4.4 Message Pointer
The message pointer points to the current message descriptor being serviced. This
pointer is maintained in a fixed memory location relative to a Group Base Pointer
in shared memory.
Table 5-21 lists the message pointers and their descriptions.
Table 5-21. Message Pointer
Bit
Field
Name
31:2
MSGPTR[29:0]
1:0
MSGPTR[1:0]
Value
0
Description
These 30 bits are appended with 00b to form a dword-aligned 32-bit address. This
word pointer points to the first dword of a Message Descriptor.
Ensures dword alignment.
100660E
Conexant
5-31