28478G-18 Mindspeed Technologies, 28478G-18 Datasheet - Page 140

• Manufacturer Part Number: 28478G-18
• Description: Multichannel Synchronous Communications Controller 208-Pin BGA
• Manufacturer: Mindspeed Technologies

Specifications of 28478G-18

• Package: 208BGA
• Maximum Data Rate: 32768 Kbps
• Transmission Media Type: Wire
• Power Supply Type: Analog
• Typical Supply Current: 250 mA
• Typical Operating Supply Voltage: 3.3 V
• Minimum Operating Supply Voltage: 3 V
• Maximum Operating Supply Voltage: 3.6 V

The Buffer Descriptor contains a set of bit fields which instruct MUSYCC how to behave after the data is put in or
taken out of a data buffer.
The Data Pointer contains an address in shared memory where MUSYCC can take data to be transmitted or store
data received from the corresponding channel.
The Next Descriptor Pointer contains an address of a Message Descriptor in shared memory where MUSYCC can
access the “next” Message Descriptor in the linked list.
To terminate a message list, the contents of the Next Descriptor Pointer in the last descriptor in a list can point
either to the address of the last descriptor or to a general purpose “terminate” Message Descriptor that can be
used by any message list to represent the end of the list. Thus, the OWNER bit field in the last descriptor’s Buffer
Descriptor must eventually indicate that the host owns the buffer. This bit value is opposite for receive and transmit
buffer ownership.
The OWNER bit field mechanism controls the termination of the message list as MUSYCC reads in each Message
Descriptor in the linked list: it first checks the OWNER bit field to see if it, and not the host, owns the buffer. If it does
own the descriptor, after servicing the contents of this descriptor, MUSYCC reverses the OWNER bit field to hand
the descriptor back to the host; if it does not own the buffer, the end of the message list is automatically concluded.
The channel stays active and, depending on other bit field values in the Buffer Descriptor, MUSYCC either polls
this last descriptor regularly to see if the OWNER bit value has changed, or it idles the channel and awaits another
channel activation or channel jump request. The former is useful in continuing a message list while retaining the
original list. The latter is useful in starting a message list from the top element in the list.
The host processor must never change a descriptor in a buffer to which it has already granted MUSYCC
ownership. The Owner bit is the only handshake mechanism to prevent race conditions.
The following describes a general sequence for setting up the transmit Message Descriptor for a single channel:
28478-DSH-002-E
/* assume transmit channel is currently deactivated */
/* assume that a 1024-byte message is separated into four 256-byte data buffers */
/* Because four buffers will be used, four 12-byte segments [or one 48-byte */
/* of shared memory is required */
/* declare structures */
typedef tDATA_BUFFER
{
unsigned char Data[256];
} DATA_BUFFER;
typedef tMSG_DESCR
{
unsigned long BufferDescr;
struct DATA_BUFFER *pDataBuffer;
struct MSG_DESCR *pNextMsgDescr;
} MSG_DESCR;
/* allocate space */
MSG_DESCR *pTxMsgDescr[4];
DATA_BUFFER *pDataBuf[4];
/* link the message descriptors together. Terminate the message list by */
/* assigning the “next” pointer in the last descriptor to point to the last */
/* descriptor itself */
pTxMsgDescr[0]->pNextMsgDescr = pTxMsgDescr[1];
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