le79128 Zarlink Semiconductor, le79128 Datasheet - Page 27

• Manufacturer Part Number: le79128
• Description: Next Generation Voiceedge™ Control Processor Next Generation Carrier Chipset Ngcc
• Manufacturer: Zarlink Semiconductor

APPLICATION LAYER
The application layer defines the programmer’s interface and is almost entirely implemented in firmware. The exception is a
handful of configuration registers implemented in hardware. This layer defines the meaning of the payload data delivered by the
transport layer. Because it is implemented in firmware, the definition of the programmer’s interface can change by providing new
software. The primary elements of the model are system registers, mailbox buffers and an event queue. The following sections
describe these elements in more detail.
Software (Application Derived) Registers
The remainder of the registers defined in the HBI register space are application defined registers. For detailed information on
these registers, refer to the VoicePath API II Reference Guide for VCP Devices.
Mailboxes Buffers
Mailbox buffers are composed of a dedicated interface page and an associated hardware semaphore flag to control ownership.
Mailbox buffers pass information in one direction only. The host writes to a downstream mailbox and reads from an upstream
mailbox. The reverse is true for the DSP. The flag indicates mailbox status and guards against race conditions.
All mailbox flags are located in the 16-bit software flag register implemented on the direct page. They exhibit the following
characteristics. Only the host can set a mailbox flag. Likewise, only the DSP can clear a mailbox flag. High-to-low transitions
generate a maskable interrupt towards the host. Low-to-high transitions generate a maskable interrupt towards the DSP.
The following steps illustrate how a mailbox is used to pass information in the downstream (i.e. host-to-DSP) direction. For an
upstream exchange, roles are simply reversed.
1. The host waits for the appropriate mailbox flag to go low, indicating that the mailbox is now empty. To do this, the host can
2. The host selects the mailbox by issuing a Select Page command.
3. The host writes data into the mailbox using either the Paged Offset or Paged Access commands. Data can be written with
4. When the host is finished writing data to the mailbox, it then sets the associated mailbox flag by writing a one to the
5. The DSP either polls the mailbox flag register, or receives an interrupt indicating data is available.
6. The DSP reads and processes the contents of the mailbox taking any required actions. It reads the first location in the mailbox
7. The DSP clears the associated mailbox flag, indicating to the host that it is finished processing and passing ownership back
Command/Response Mailboxes
This mailbox pair provides a channel for exchanging command and status messages with the host. Refer to the VP-API code for
commands. The command mailbox is for the host to write commands. The response mailbox is for the DSP to report the results
of read commands or confirmation of write commands.
Event Queue
A key element of the host interface is an event queue. Events relay asynchronous information back to the host. Buffering events
in a queue gives the host flexibility on when to read them, and ensures that no events are lost if the host is unable to service them
immediately.
The host reads the event queue through the interrupt indication and parameter registers. Events are composed of a 16-bit
indication value that includes channel and event type fields, and an optional 16-bit parameter. Several of the Le79128 VCP events
require a 32-bit timestamp. The timestamp can be reduced to 16-bits by creating a timestamp rollover event, and letting the host
maintain the upper 16-bits. An event reports the lower 16-bits of the timestamp in the parameter register. (See the VP-API II
User’s Guide for information on an event associated with a timestamp).
either poll the mailbox flag register, or unmask the associated interrupt and wait for an interrupt to be generated.
one command or with several. The first location of the mailbox is used to indicate the length of the data being passed to the
DSP. The host is responsible for writing this length value.
appropriate bit in the mailbox flag register. This indicates to the DSP that data is waiting in the mailbox, and ownership has
passed to the DSP.
to determine the length of the data.
to the host.
Microsemi Corporation - CMPG
Le79128
27
Preliminary Data Sheet