CN8478 Datasheet, PDF (106/221 Pages) Conexant Systems, Inc – Multichannel Synchronous Communications Controller (MUSYCC)

5.0 Memory Organization
5.2 Descriptors
CN8478/CN8474A/CN8472A/CN8471A
Multichannel Synchronous Communications Controller (MUSYCC™)
5.2.2.6 Message Length
Descriptor
Each channel group can have two separate values for maximum message length:
MAXFRM1 or MAXFRM2 (see Table 5-13). The maximum message length is
4,094 octets. The minimum message length is either 1, 3, or 5 depending on
non-FCS mode or FCS16 or FCS32 support, respectively. Each receive channel
either selects one of these message length values or disables message length
checking altogether.
The MAXSEL bit field (see Table 5-18, Channel Configuration Descriptor)
selects which, if any, register is used for received-message length checking. If
MUSYCC receives a message exceeding the allowed maximum, the current
message processing is discontinued and terminates further transfer of data to
shared memory. In addition, a Receive Buffer Status Descriptor, corresponding to
the partially received message, indicates a Long Message error condition, and an
interrupt descriptor is generated towards the host indicating the same error
condition.
NOTE: The equation that defines maximum message length without generating a
LNG error is:
Maximum Message Length = MAXFRM – FCS where FCS = 2 bytes for
HDLC-16 protocol and FCS = 4 bytes for HDLC-32 protocol.
In the case of a short message (bit count less than 3 or 5 octets), data is not
transferred into shared memory and is discarded. In addition, an interrupt
descriptor is generated towards the host, indicating the same error condition.
Table 5-13. Message Length Descriptor
Bit
Field
Name
Value
31:28
RSVD
0
27:16 MAXFRM2[11:0]
15:12
RSVD
0
11:0 MAXFRM1[11:0]
Description
Reserved.
Defines a limit for the maximum number of octets allowed in a received HDLC
message.
Valid values for the register range from 3 to 4094 depending on FCS16 or
FCS32.
Reserved.
Defines a limit for the maximum number of octets allowed in a received HDLC
message.
Valid values for the register range from 3 to 4094 depending on FCS16 or
FCS32.
5.2.2.7 Time Slot Map
The time slot map consists of 32 time slot descriptors. One descriptor maps four
time slots. The entire map contains configuration information for 128 time slots.
The serial port does not need to support 128 time slots all the time. Any number
of time slots from 1 to 128 is supportable.
The time slot map is used when the serial port associated with a channel group
is configured in one of the channelized modes: T1, E1, 2xE1, 4xE1, or Nx64.
MUSYCC supports mapping of up to 128 time slots from a channelized bit
stream with up to 32 logical channels in each channel group.
5-20
Conexant
100660E