cx28500 Mindspeed Technologies, cx28500 Datasheet - Page 88

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

The availability of the device to the Host for access is an example of information provided by querying the Service
Request Length register. After the PCI reset, CX28500 sets the SRQ_LEN field in Service Request register to all
1s or 0x3FF, until it performs all the internal initialization. Since the Host cannot modify the Service Request Length
register while it is non-0, the setting of this register to all 1s by CX28500 effectively prevents the Host from making
additional service requests that could interfere with its internal initialization. When CX28500 is finished with the
internal initialization, it clears this field to 0. The cleared SRQ_LEN indicates to the Host that it is ready. From this
point, the Host is able to directly write this field with the actual number of service requests that CX28500 needs to
perform to configure its registers. The number of SRQs written by the Host is stored in the SRQ_LEN field. While
processing the service request commands, the SRQ_LEN field indicates how many commands are yet to be
processed by CX28500 before a new command can be issued. Host slave writes to this register triggers the
execution of the service request list specified by the Service Request Pointer register.
Table 6-3.
The Service Request Pointer register provides the address of the Service Request Descriptor Table (see
4). Host needs to allocate and initialize this table in shared memory.
Table 6-4.
6.2.1.1
A Service Request Descriptor (SRD) is a 4-dword location in shared memory. Actually, one represents an entry in
the SRD table. The SRD is defined as a union type in C, which allows different commands to be configured in a 4-
dword space. The SRD can handle three different configurations: Device Configuration Descriptor (DCD), EBUS
Configuration Descriptor (ECD), and Channel Configuration Descriptor (CCD).
28500-DSH-002-C
31:10
31:3
Bit
9:0
Bit
2:0
SRQ_PTR [31:3]
SRQ_PTR [2:0]
SRQ_LEN [9:0]
Field Name
Field Name
Service Request Length Register
Service Request Pointer Register
RSVD
NOTE:
Service Request Descriptor
Host slave writes to SRQ_LEN field, while the previous list of service requests has not been
processed (i.e., SRQ_LEN is reset) implies unpredictable behavior.
Value
Value
—
—
0
0
Mindspeed Proprietary and Confidential
Mindspeed Technologies
Service Request Pointer. These 29 bits are appended with 000b to form a 64-bit address Quadword
aligned. This address points to the first entry on the Service Request Descriptor Table allocated in
shared memory.
To ensure Quadword alignment.
Reserved.
Service Request Length.
After a PCI reset, Host reads the SRQ_LEN bit field through PCI slave access. While the SRQ_LEN
value equals 0x3FF, CX28500 is not ready to start the configuration of the device. If CX28500 resets
this value, the device is ready to be configured. Host directly writes at this location the number of
Service Request Descriptors (SRD) which were allocated in Service Request Descriptor Table
(SRDT) i.e., shared memory. The SRDs was previously initialized and configured in SRDT. This value
represents the number of service request commands queued by Host (i.e., the SRDT), that are
waiting to be performed. Real-time reads from SRQ_LEN provides the number of service request
commands that are waiting to be served.
Do not write SRQ_LEN until after the SRQ_PTR, or the address of the Service Request Descriptor
Table, is initialized. Because CX28500 starts to process service requests whenever SRQ_LEN is non-
0 by modifying SRQ_LEN to the non-0 before a valid SRQ_PTR is written, CX28500 processes the
invalid SRQ_PTR, resulting in unpredictable behaviors.
®
Description
Description
Memory Organization
Table 6-
73