cx28500 Mindspeed Technologies, cx28500 Datasheet - Page 128

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

suspended for the channel. The Host must use the Host service mechanism (channel activation or channel jump
commands) in order to continue DMA handling for the channel.
The ONR-bit mechanism prevents CX28500 from processing the same buffer twice without intervention from the
Host.
Additionally, the Host can append additional information beyond the end of a data buffer as long as the longest
message length can be fitted first into the data buffer. In the case of additional information, it is ignored.
For simplicity, the following discussion is made in reference to one channel. Each channel is serviced
independently of another channel, and separate message descriptor tables are maintained for each supported
channel.
Similarly, both transmit and receive sections of a channel service the descriptor tables identically, and separate
message descriptor tables are maintained for each section. Also, the size of data fields in the descriptors is
identical; however, the layout of fields between receive and transmit descriptors is different.
6.8.6
The Buffer Descriptor (BD) resides in the shared memory and is fetched by CX28500 each time a new data buffer
is required. All Buffer Descriptors include the following fields:
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The ONR bit is a generic term for any descriptor. In a Transmit Buffer Descriptor it is generically called CX28500-
owned. In a Receive Buffer Descriptor it is generically called Host-owned. The names are different to indicate that
the active sense of the ONR bit is different between transmit and receive functions.
In addition to the above list of fields, Transmit Buffer Descriptors include the following fields:
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IC and PADCNT are valid only when EOM = 1.
Tables 6-40
Table 6-40.
28500-DSH-002-C
31
30
Bit
Owner Indicator Bit (ONR)
No Poll/Poll Indicator (NP)
End Of Buffer Interrupt Enable (EOBIEN)
Last MD in the table (LAST)
Buffer Length (BLEN)
End Of Message Indicator (EOM)
Idle Code Selection (IC)
Pad Count (PADCNT)
and
Field Name
Transmit Buffer Descriptor (1 of 2)
ONR
6-41
NP
Buffer Descriptors
list the transmit and receive buffer descriptors and definitions.
Value
0
1
0
1
HOST Owns Buffer. Channel is to remain in idle mode while polling this bit periodically (if NP = 0) until
Host relinquishes control to CX28500 by setting ONR = 1.
CX28500 Owns Buffer. Continue processing data buffer normally.
Poll Enabled. If ONR = 0, Host-owned, CX28500 polls the message descriptor periodically while in idle
mode until ONR = 1.
Poll Disabled. If ONR = 0, then enter suspend mode and wait for a Channel Activate or Jump Host
Service from Host.
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Description
Memory Organization
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