cx28500 Mindspeed Technologies, cx28500 Datasheet - Page 140

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

4. CX28500 reads DATA from the memory buffer to internal FIFO until either an End Of Message (EOM) is
5. CX28500 transmits the read data as an HDLC frame, or as a transparent frame depending on the type of
6. CX28500 checks INHTBSD bit field:
7. CX28500 checks last bit field:
8. CX28500 reads the next message descriptor. Go to step 3.
7.2.1.2
The following describes what CX28500 does when receive channel is activated.
1. All internal FIFOs are flushed CX28500 reads Rx Head Pointer for channel from shared memory and stores it
2. Simultaneously, the receiver is configured and data is sampled in from serial port using control lines. CX28500
3. CX28500 reads Message Descriptor (Receive Buffer Descriptor and Data Pointer) pointed to by the fetched Rx
4. CX28500 checks bit field OWNER and NP in Receive Buffer Descriptor.
28500-DSH-002-C
d. If NP is 1, then TDMA does not poll the current BD, and this channel remains suspended until one of
fetched or the entire memory buffer (BLEN) is read. This is not true for transmission. In the transmit direction,
CX28500 reads all valid data buffers regardless of EOM.
protocol selected for the channel.
If INHTBSD = 0, CX28500 overwrites the Buffer Descriptor (BD) with a Buffer Status Descriptor (BSD) file, do
not write Buffer Status Descriptor (BSD).
If the buffer contains an EOM, the TSLP posts a TxEOM interrupt (if EOMIEM unmasked).
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in internal channel descriptor map.
does not pass the control to the Host memory (i.e., it does not move to step 3) until enough data is
accumulated in its internal buffers (i.e., the threshold programmed for this channel gets crossed). If HDLC
mode is selected, the RSIU will scan for an opening flag.
Head Pointer and stores in internal channel descriptor memory.
If OWNER = 0, CX28500 is the buffer owner, go to step 5. If OWNER = 1, CX28500 is not the buffer owner and
RDMA buffer processing for this channel is temporarily suspended. There are several ways for RDMA to exit
the channel suspend state:
a. Channel is instructed to jump to a new MD list (see Channel Jump).
b. Channel is instructed to reactivate to a new MD list, go to step 1.
c. While NP is 0, RDMA polls current BD until OWNER = 0, go to step 5.
d. If NP is 1, then RDMA does not poll the current BD, and this channel goes to suspended until one of
conditions a. through b. are satisfied. If CX28500 is in the middle of transmitting a message and the NP bit
becomes 1, the TDMA generates a TxONR interrupt (if ONREIM is unmasked).
If Last = 0, CX28500 advances the current MD pointer.
If Last = 1, CX28500 sets current MD pointer equal to Head Pointer.
conditions a through b are satisfied). If CX28500 is in the middle of receiving a message and the NP bit
becomes 1, the RDMA generates a RxONR interrupt (if ONRIEN is unmasked).
NOTE:
Receive Channel Activation
Because transmit EOB and EOM interrupts are independent events if the buffer contains an
EOM, two interrupts are generated, an EOB interrupt when the last data byte is read into
internal memory, and an EOM interrupt when the last data byte is transferred from the
internal memory to the Serial Interface Unit.
If the buffer is not EOM, CX28500 posts a TxEOB interrupt (if EOBIEN is set).
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Functional Description
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