Rainbow Electronics DS3134 - Manual (Page 78)

DS3134
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SECTION 6: HDLC
6.1 GENERAL DESCRIPTION
The DS3134 contains two different types of HDLC controllers. Each port has a Slow HDLC Engine (type
#1) associated with it that can operate in either a channelized mode up to 8.192 Mbps or an unchannelized
mode at rates up to 10 Mbps. Ports 0 and 1 also have associated with them, an additional Fast HDLC
Engine (type #2) that is capable of operating in only an unchannelized fashion up to 52 Mbps. Via the
Layer One registers (see Section 5.2), the Host will determine which type of HDLC controller will be
used on a Port and if the HDLC controller is to be operated in either a channelized or unchannelized
mode. If the HDLC controller is to be operated in the channelized mode, then the Layer One registers
(see Section 5.3) will also determine which HDLC channels are associated with which DS0 channels. If
the Fast HDLC Engine is enabled on Port 0, then HDLC Channel 1 is assigned to it and likewise HDLC
Channel 2 will be assigned to the Fast HDLC Engine on Port 1 if it is enabled.
The HDLC controllers are capable of handling all the normal real-time tasks required. Table 6.1B lists all
of the functions supported by the Receive HDLC and Table 6.1C lists all of the functions supported by the
Transmit HDLC. Each of the 256 HDLC channels within Chateau are configured by the Host via the
Receive HDLC Channel Definition (RHCD) and Transmit Channel Definition (THCD) registers. There
is a separate RHCD and THCD register for each HDLC channel. The Host can access the RHCD and
THCD registers indirectly via the RHCDIS indirect select and THCDIS indirect select registers. See
Section 6.2 for details.
On the receive side, when the HDLC Block is processing a packet, one of the outcomes shown in
Table 6.1A will occur. For each packet, one of these outcomes will be reported in the Receive Done
Queue Descriptor (see Section 8.1.4 for details). On the transmit side, when the HDLC Block is
processing a packet, an error in the PCI Block (parity or target abort) or transmit FIFO underflow will
cause the HDLC Block to send an Abort sequence (8 ones in a row) followed continuously by the selected
Interfill (either 7Eh or FFh) until the HDLC channel is reset by the transmit DMA Block (see Section
8.2.1 for details). This same sequence of events will occur even if the transmit HDLC channel is being
operated in the transparent mode. In the transparent mode, when the FIFO empties the device will send
either 7Eh or FFh.
Receive HDLC Packet Processing Outcomes Table 6.1A
Outcome Criteria
EOF / Normal
Packet Integral number of packets > min. & < max. is received & CRC is okay
EOF / Bad FCS Integral number of packets > min. & < max. is received & CRC is bad
Abort Detected Seven or more ones in a row detected
EOF / Too Few
Bytes Less than 4 or 6 bytes received
Too Many Bytes Greater than the packet maximum is received (if detection enabled)
EOF / Bad # of Bits Not an integral number of bytes received
FIFO Overflow Tried to write a byte into an already full FIFO