cx28500 Mindspeed Technologies, cx28500 Datasheet - Page 139

• Manufacturer Part Number: cx28500
• Description: Cx28500 Multichannel Synchronous Communications Controller
• Manufacturer: Mindspeed Technologies

7.2
7.2.1
Channel Activation is an asynchronous command from the Host interface to a transmit or receive section of a
channel to jump to a new message. Message Descriptors in shared memory describe the attributes of the new
message, what to do between messages, and identify the location of message data buffers in memory to use for
transmit data or receive data.
After the previous levels of configuration are completed, individual channels are ready to be activated. Service
requests are used to activate channels.
Each channel consists of a transmitter and a receiver section. Each section is independent of the other and
maintains its own state machine, configuration registers, and internal resources. To activate both transmitter and
receiver sections, two separate service requests are required, one directed to the transmitter and one to the
receiver. CX28500 responds to each service request with the SACK Interrupt Descriptor, which notifies the Host
that the task was initiated. The notification to the Host that the task was completed is an EOCE interrupt. This
acknowledges the Host that the SRQ was completed. Upon channel activation, CX28500 flushes out all internal
FIFO’s, SLP’s, and DMA’s, then, updates their head pointer tables.
7.2.1.1
The following describes what CX28500 does when the transmit channel is activated.
1. CX28500 reads Tx Head Pointer for channel from shared memory and stores it in the internal channel
2. CX28500 reads Message Descriptor (buffer descriptor and data pointer) pointed to by the fetched Tx Head
3. CX28500 checks bit field OWNER and NP in Buffer Descriptor.
28500-DSH-002-C
descriptor map, and generates an EOCE interrupt if it’s enabled.
Pointer and stores it in internal channel descriptor memory. The actual read of the Message Descriptor
depends on crossing a threshold in the internal transmit FIFO. In this case, however, because the activation
command empties the internal transmit FIFO, which causes it to cross the FIFO threshold, it is guaranteed that
the message descriptor is read.
If OWNER = 1, CX28500 is buffer owner. Go to step 4.
If OWNER = 0, CX28500 is not the buffer owner and TDMA buffer processing for this channel is temporarily
suspended. There are several ways of TDMA to exit the channel suspended state:
a. Channel is instructed to jump to a new MD list (see CH-JUMP).
b. Channel is instructed to reactivate to a new MD list, go to step 1.
c. While NP is zero, TDMA polls current BD until OWNER = 0, go to step 4.
NOTE:
Channel Operations
Channel Activation
Transmit Channel Activation
The steps [1] to [17] can be performed in one single step by setting the Service Request
Table with two entries and waiting for only one SACK or ECI. This increases the
performance over the PCI bus.
19. Perform a CH_ACT Service Request and wait for SACK when the SACKIEN bit is set.
For each channel that needs to be activated, the Host prepares a CH_ACT Service
Request and inserts it into the Service Request Table. The Host may decide to activate
all channels by writing the Service Request queries into one single Service Request
table or by splitting the service request commands into one or more tables. For each
CH_ACT Service Request the Host follows the same steps as were specified at [13.1]
through [13.4]
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Functional Description
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