cx28560 Mindspeed Technologies, cx28560 Datasheet - Page 118

• Manufacturer Part Number: cx28560
• Description: Hdlc Controller
• Manufacturer: Mindspeed Technologies

The CX28560 Memory Organization
5.7.3
Table 5-26. Maximum Message Length Register
5-28
NOTE(S):
MAXSEL-bit in the configuration memory) is inactive.
31:14
13:0
Bit
The host may change the value of Maximum Message Length register only if the channel that uses its value (according to
RSVD
RMAXFRM[13:0]
Field Name
The RSLP Maximum Message Length register, defined in
values for maximum message length: MAXFRM1, MAXFRM2, and MAXFRM 3. Their structure
is shown in RSLP Channel Configuration register. The minimum message length is either 1, 3, or 5
depending on protocol mode: no FCS, 16-bit FCS, or 32-bit FCS, respectively. In the case of a
short message, data is not transferred to the host but instead is discarded. In addition, an interrupt
descriptor is generated toward the host indicating the short error condition. Note, a bit stream that
contains messages of length less than 40 Bytes requires the CX28560 to be configured with large
buffers. Although the CX28560 can work with small messages, the buffer calculations and
bandwidth calculations have to be re-examined.
Each receive channel either selects one of these message length values or disables message length
checking altogether.
The MAXSEL bit field (see
message length checking. If the CX28560 receives a message exceeding the allowed maximum,
the current message processing is discontinued and terminates further transfer of data to the host.
In addition, a Receive Message Header, corresponding to the partially received message, indicates
a Long Message error condition, and an interrupt descriptor is generated toward the host indicating
the same error condition.
RSLP Maximum Message Length Register
Value
—
0
Reserved.
Defines a limit for the maximum number of bytes allowed in a received HDLC message.
Valid values for the register range from 0 to 16 K – 1.
The formula to set MAXFRM is:
MAXFRM = Max Allowed Message Length (bytes) + FCS (bytes) – 2.
Where:
FCS = 0 for Non-FCS Mode
FCS= 2 byte for HDLC-16 Mode
FCS = 4 byte for HDLC-32 Mode.
A Too Long Message interrupt is generated when the number of bytes in the processed
message exceeds Max Allowed Message Length.
Mindspeed Technologies™
Table
Advance Information
5-25) selects which (if any) register is used for received
Description
Table
5-26, can have three separate
CX28560 Data Sheet
28560-DSH-001-B