CN8478 Datasheet, PDF (156/221 Pages) Conexant Systems, Inc – Multichannel Synchronous Communications Controller (MUSYCC)

6.0 Basic Operation
6.3 Channel Operation
CN8478/CN8474A/CN8472A/CN8471A
Multichannel Synchronous Communications Controller (MUSYCC™)
6.3.16.2 Receive
Channel Activation
4. Checks bit field INHTBSD in Group Configuration Descriptor.
If INHTBSD = 0 (i.e., MUSYCC is allowed to overwrite Buffer Descriptor
with a Buffer Status Descriptor), the address of the Buffer Descriptor is
stored in the Message Pointer slot in shared memory. After the current
message is completely processed, MUSYCC reads in the Next Message
Pointer and overwrites Buffer Descriptor. Go to 3.
If INHTBSD = 1 (i.e., MUSYCC is not allowed to overwrite Buffer
Descriptor), the address of Next Message Pointer is pre-fetched from the
current Message Descriptor and stored in the Message Pointer slot in
shared memory. After the current message is completely processed,
MUSYCC jumps to this pointer and starts processing a new message.
Go to 5 when current message is processed, otherwise repeat 4.
Simultaneously, MUSYCC masters the PCI bus and reads data into
transmit FIFO from shared memory, and the serial port outputs data using
the control lines TCLK, TSYNC, and TDAT as appropriate.
5. At end of message, Interrupt Descriptors and Buffer Status Descriptors can
be written out to shared memory (see 3)—depending on the masking of
interrupts and allowance of Buffer Descriptor overwrites.
6. Read Next Message Descriptor.
7. Go to 3.
The following describes what MUSYCC does when the receive channel is
activated:
1. Reads the Rx Head Pointer for the specified channel from shared memory,
and stores in the Internal Channel Descriptor map.
2. Reads the Message Descriptor pointed to by Head Pointer, and stores in the
Channel Descriptor map.
3. Check bit field OWNER and NP in Buffer Descriptor.
If OWNER = 0, MUSYCC is the buffer owner. Load Channel Descriptor
map with data buffer pointer and data buffer length. Go to 4.
If OWNER = 1, MUSYCC is not the buffer owner. May enter polling
mode until MUSYCC owns buffer or receives another service request to
activate channel. Repeat 3.
4. Check bit field INHRBSD in Group Configuration Descriptor.
If INHRBSD = 0 (i.e., MUSYCC is allowed to overwrite Buffer Descriptor
with a Buffer Status Descriptor), the address of the Buffer Descriptor is
stored in the Message Pointer slot in shared memory. After current
message is completely processed, MUSYCC reads in Next Message
Pointer and overwrites Buffer Descriptor. Go to 3.
If INHRBSD = 1 (i.e., MUSYCC is not allowed to overwrite Buffer
Descriptor), the address of Next Message Pointer is pre-fetched from the
current Message Descriptor and stored in the Message Pointer slot in
shared memory. After the current message is completely processed,
MUSYCC jumps to this pointer and starts processing the new message.
Go to 5 when current message is processed, otherwise repeat 4.
Simultaneously, the receiver is configured and data is sampled in from the
serial port using control lines RCLK, RSYNC, RDAT, and ROOF as
appropriate, and, MUSYCC masters the PCI bus and transfers data from
the internal FIFO to shared memory.
6-22
Conexant
100660E