Freescale Semiconductor
Application Note
AN2147
Rev. 2, 11/2004
Initializing MSC8101/MSC8103 CPM
Parameter RAM and Buffer
Descriptors
By Barbara Johnson
When using the MSC8101/MSC8103 communications
processor module (CPM) serial controllers, you must initialize
the parameter RAM, buffer descriptor tables, and data buffers. It
is important that you understand the structure of the parameter
RAM and buffer descriptor tables as you define the parameters
for the operation of the serial controller and allocate the data
buffers. All serial controllers have a common structure that
includes the following protocols:
•
Serial communications controllers (SCCs): UART, HDLC,
BISYNC, Transparent, Ethernet, and AppleTalk modes
•
Fast communications controllers (FCCs): HDLC, Fast
Ethernet, and Transparent modes
•
Serial management controllers (SMCs): UART,
Transparent, and GCI modes
•
Multi-channel controllers (MCCs): HDLC and Transparent
modes
•
Serial peripheral interface (SPI)
•
Inter-integrated circuit (I2C)
This application note describes the structure of the parameter
RAM and buffer descriptors and provides examples in C for
defining them.
© Freescale Semiconductor, Inc., 2001, 2004. All rights reserved.
CONTENTS
1
1.1
1.2
1.3
2
2.1
2.2
3
3.1
3.2
4
4.1
4.2
5
6
Parameter RAM ......................................................2
Parameter RAM Memory Map ...............................2
General Parameters .................................................3
SCC Parameter RAM Example ...............................4
Buffer Descriptors ...................................................4
Buffer Pointer ..........................................................5
BD Naming Conventions ........................................5
BD and Buffer Memory Structure .......................... 6
SCC2 Example ........................................................6
SPI Example ............................................................7
Initialization Examples ...........................................8
Parameter RAM ...................................................... 8
Buffer Descriptors and Data Buffers ...................... 9
RxBD Processing Example .....................................9
TxBD Processing Example ...................................11
Parameter RAM
1
Parameter RAM
The parameter RAM is a section of memory located in Banks 9 and 10 of the dual-port RAM, as shown in Table 1.
Each bank is 2 KB. Bank 9 is located at an offset of 0x8000 from the Internal Space Base (ISB) which is defined in
the Internal Memory Map Register (IMMR). Bank 10 is located at an offset of 0x8800 from ISB. For example, if
the IMMR = 0x14705000, then the ISB is at address 0x14700000. The absolute start addresses of Bank 9 and Bank
10 are 0x14708000 and 0x1478800, respectively.
Table 1. Dual-Port RAM Memory Map
Offset from ISB
Bank
Storage
Size
0x0000
1
BD/Data/Code
2 KB
0x0800
2
BD/Data/Code
2 KB
0x1000
3
BD/Data/Code
2 KB
0x1800
4
BD/Data/Code
2 KB
0x2000
5
BD/Data/Code
2 KB
0x2800
6
BD/Data/Code
2 KB
0x3000
7
BD/Data/Code
2 KB
0x3800
8
BD/Data/Code
2 KB
0x4000
Reserved
16 KB
0x8000
9
Parameter RAM
2 KB
0x8800
10
Parameter RAM
2 KB
0x9000
Reserved
8 KB
0xB000
11
FCC Data
2 KB
0xB800
12
FCC Data
2 KB
1.1 Parameter RAM Memory Map
The MSC8101/MSC8103 parameter RAM structure memory map is shown in Table 2. Because the exact
definition of the parameter RAM differs for each protocol, the number of parameters for each protocol varies. For
example, SCC1 has 256 bytes allocated for parameters but the SCC1 UART protocol uses only 102 bytes and the
SCC1 HDLC protocol uses only 92 bytes. Unused parameter RAM can be used for storage area for data buffers.
Some protocols, such as SMCx, SPI, and I2C have only two bytes allocated for storage in the parameter RAM.
Parameters are not stored in these two bytes. Instead, these two bytes contain a user-programmable pointer to the
location where the parameters are stored. For example, ISB+0x8AFC contains a pointer to the I 2C parameters that
can be placed in the dual-port RAM.
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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Parameter RAM
Table 2. Parameter RAM Memory Map
Bank
Bank
9
Offset
from ISB
Peripheral
Size
(Bytes)
Offset
from ISB
Peripheral
Size
(Bytes)
0x8000
SCC1
256
0x8800
MCC2
128
0x8100
SCC2
256
0x88FC
SMC2
2
0x8200
SCC3
256
0x88FE
IDMA2
2
0x8300
SCC4
256
0x89FC
SPI
2
0x8400
FCC1
256
0x89FE
IDMA3
2
0x8500
FCC2
256
0x8AE0
RISC
Timers
16
0x8600
FCC3
256
0x8AF0
REV_NUM
2
0x8700
MCC1
128
0x8AF8
RAND
4
2
2
Bank
Bank
10
0x87FC
SMC1
2
0x8AFC
I2C
0x87FE
IDMA1
2
0x8AFE
IDMA4
1.2 General Parameters
Although each protocol has a different set of parameters, some parameters are shared by many protocols. This
section describes parameters that are common to many protocols:
•
RBASE and TBASE. Define the base addresses for the receive buffer descriptor (BD) and the transmit
BD. These parameters define the starting location in the memory map for the BDs. RBASE and
TBASE are each 32 bits long when the FCC controller is used and 16 bits long when any controller
other than the FCC is used. These parameters define the offset from the beginning of dual-port RAM.
The BD tables can be placed in Banks 1 – 8 of the dual-port RAM or in any unused parameter RAM
area. Because each BD is 8 bytes, RBASE and TBASE values should be multiples of 8.
•
RBPTR and TBPTR. During frame processing, RBPTR points to the current receive BD. In idle state,
RBPTR points to the next receive BD. Similarly, TBPTR points to the current transmit BD during
frame transmission and to the next transmit BD in idle state.
•
RFCR and TFCR. Specify byte ordering, transfer code, and bus location of data and BDs. The same
information is specified in RSTATE and TSTATE when the FCC controller is used.
•
MRBLR. Defines the maximum number of bytes the receiver writes to a receive buffer before moving
to the next buffer. The receiver can write fewer bytes than MRBLR if an error condition or an end-offrame occurs. It never writes more bytes than the MRBLR value, so the user-supplied buffers should
be at least as large as the MRBLR. The MRBLR should be greater than zero. The size of the transmit
buffers is not affected by the MRBLR value. The MRBLR should not be changed dynamically while
the receiver is operating.
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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3
Buffer Descriptors
1.3 SCC Parameter RAM Example
Table 3 shows the parameter RAM for all SCC protocols. The boldfaced entries are the parameters that you must
initialize in order to enable the SCC. Refer to the product reference manual for the protocol-specific parameters.
Table 3. SCC Parameter RAM
Offset from
ISB+0x8000
Name
Width
Description
0x00
RBASE
16 bits
0x02
TBASE
16 bits
RxBD/TxBD table base address. Offset from the beginning of dual-port RAM. The
BD tables can be placed in any unused portion of Banks 1 – 8. The CP starts BD
processing at the top of the table. These values need to be initialized before the
corresponding channels are enabled. RBASE and TBASE values must be multiples
of 8.
0x04
RFCR
8 bits
0x05
TFCR
8 bits
0x06
MRBLR
16 bits
Maximum receive buffer length. Defines the maximum number of bytes the
MSC8101/MSC8103 writes to a receive buffer before it goes to the next buffer. The
MSC8101/MSC8103 can write fewer bytes than MRBLR if an error or an end-offrame occurs. It never writes more bytes than the MRBLR value. MRBLR should be
changed only while the receiver is disabled.
0x08
RSTATE
32 bits
Rx internal state. For CP use only.
0x0C
—
32 bits
Rx internal buffer pointer. Updated by the SDMA channels to show the next
address in the buffer to be accessed.
0x10
RBPTR
16 bits
Current RxBD pointer. Points to the BD being processed or to the next BD the
receiver uses when it is idling. After reset or when the end of the BD table is
reached, the CP initializes RBPTR to the value in RBASE.
0x12
—
16 bits
Rx internal byte count. Down-count value initialized with MRBLR and
decremented with each byte written by the supporting SDMA channel.
0x14
—
32 bits
Rx temp. For CP use only.
0x18
TSTATE
32 bits
Tx internal state. For CP use only.
0x1C
—
32 bits
Tx internal buffer pointer. Updated by the SDMA channels to show the next
address in the buffer to be accessed.
0x20
TBPTR
16 bits
Current TxBD pointer.
0x22
—
16 bits
Tx internal byte count. Down-count value initialized with TxBD.length and
decremented with each byte read by the supporting SDMA channel.
0x24
—
32 bits
Tx temp. For CP use only.
0x28
RCRC
32 bits
0x2C
TCRC
32 bits
Temp receive/transmit CRC. Does not need to be accessed for normal operation
but may be helpful for debugging.
0x30
—
2
Rx/Tx function code. Contains the transaction specification associated with
SDMA channel accesses to external memory.
Protocol-specific area.
Buffer Descriptors
A BD contains the essential information about each buffer in memory. Each buffer is referenced by a BD that can
reside anywhere in dual-port RAM. Each 64-bit BD has the structure shown in Figure 1. This structure is common
to all the serial controllers. A receive BD (RxBD) table and a transmit BD (TxBD) table are associated with each
serial controller. A BD table can have one or more BDs. The base address of the BDs is defined in the RBASE and
TBASE parameters and should be multiples of 8 bytes.
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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Buffer Descriptors
Figure 1. Buffer Descriptor Structure
Offset from RBASE or
TBASE (multiple of 8)
0
1
2
3
4
5
6
7
8
9
10
0x0
Status and Control
0x2
Data Length
0x4
High-Order Buffer Pointer
0x6
Low-Order Buffer Pointer
11
12
13
14
15
•
Status and Control. The 16-bit value at offset+0x0 contains status and control bits that control and
report status information on the data transfer. The CPM updates the status bits after the buffer is sent or
received. Only this field differs for each protocol. Refer to the product reference manual for each
protocol’s status and control field bit descriptions.
•
Data Length. The 16-bit value at offset+0x2 contains the number of bytes sent or received.
•
RxBD Data Length. The number of bytes the communications processor (CP) writes into the RxBD
buffer once the BD closes. The CP updates this field after the received data is placed into the buffer
and the buffer is closed. You do not need to initialize this field.
•
In frame-based protocols, except for the SCC transparent mode, the RxBD data length field contains
the total frame length including CRC bytes. If a received frame’s length, including CRC, is an exact
multiple of the parameter RAM maximum receive buffer length MRBLR, the last BD’s buffer holds
no actual data but the BD contains the total frame length.
•
TxBD Data Length. The number of data bytes the controller needs to transmit from its buffer. The CP
never modifies this field. You must initialize this field.
2.1 Buffer Pointer
The 32-bit data at offset+0x4 points to the beginning of the buffer in internal or external memory. For an RxBD the
buffer pointer value must be a multiple of four to be word-aligned. For a TxBD the buffer pointer value can be even
or odd.
2.2 BD Naming Conventions
In this discussion, the BD type and field values use the convention BD.field. Table 1 shows the possible BD
and field values. Individual bits in the BD status and control field are referred to as BD.cstat.bit. Consult the
product reference manual for the specific protocol’s status and control field bit definition.
Table 4. Buffer Descriptor Name Convention
BD Name
RxBD or TxBD
Field Name
cstat
Status and Control
length
Data Length
addr
Address Pointer
Examples of BD naming conventions are as follows:
•
TxBD.cstat.R refers to the ready bit in the TxBD’s status and control field.
•
RxBD.length refers to RxBD’s data length field.
•
RxBD.addr refers to RxBD’s buffer pointer field.
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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5
BD and Buffer Memory Structure
3
BD and Buffer Memory Structure
The BDs of all protocols can point to data buffers located in the internal dual-port RAM. Banks 1–8, which are
located at ISB+0x0 through ISB+0x4FFF, are available for storing BDs and their buffers. However, if the data
buffers are large, they can be located in external memory.
3.1 SCC2 Example
Figure 2 shows that the SCC2 parameter RAM is located at ISB+0x8100. The RBASE parameter contains a
pointer to the base address of the RxBD table that is located in the dual-port RAM at ISB+0. Since there are three
RxBDs, the first RxBD is located at ISB+0x0, the second is located at ISB+0x08, and the third is located at
ISB+0x10. The TBASE parameter contains a pointer to the base address of the TxBD table. Since the TxBD table
immediately follows the RxBD table, the first TxBD table is located at ISB+0x18, the second is at ISB+0x20, and
the third is located at ISB+0x28. RxBD.addr contains a pointer to the receive buffer in external memory, and
TxBD.addr contains a pointer to the transmit buffer in external memory.
Dual-Port RAM
RxBD Table
ISB+0x0000
ISB+0x0018
SCC2 RxBD Table
RxBD.cstat
SCC2 TxBD Table
RxBD.length
External
Memory
RxBD.addr
Rx Buffer
TxBD Table
TxBD.cstat
SCC2 Parameters
RBASE
ISB+0x8100
TxBD.length
TxBD.addr
Tx Buffer
TBASE
SCC2
Parameter RAM
RFCR
TFCR
MRBLR
RSTATE
RBPTR
TSTATE
TBPTR
RCRC
TCRC
ProtocolSpecific
Figure 2. SCC2 BD and Buffer Memory Structure
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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BD and Buffer Memory Structure
3.2 SPI Example
Figure 3 shows that the 2-byte SPI_BASE parameter RAM is located at ISB+0x89FC, which contains a pointer to
the SPI parameter table. The SPI parameter table can be placed at any 64-byte aligned address in the dual-port
RAM’s general-purpose area or in Banks 1–8. In the example presented here, the parameter table is placed at
ISB+0x0100. The RBASE parameter contains a pointer to the base address of the RxBD table, which is located in
the dual-port RAM at ISB+0. Since there are three RxBDs, the first RxBD is located at ISB+0x0, the second is
located at ISB+0x08, and the third is located at ISB+0x10. The TBASE parameter contains a pointer to the base
address of the TxBD table. Since the TxBD table immediately follows the RxBD table, the first TxBD table is
located at ISB+0x18, the second is at ISB+0x20, and the third is at ISB+0x28.
RxBD.addr contains a pointer to the receive buffer in external memory, and TxBD.addr contains a pointer to
the transmit buffer in external memory.
RxBD Table
Dual-Port RAM
ISB+0x0000
ISB+0x0018
SPI RxBD Table
RxBD.cstat
SPI TxBD Table
RxBD.length
External
Memory
RxBD.addr
ISB+0x0100
TxBD Table
SPI
Parameter Table
Rx Buffer
TxBD.cstat
TxBD.length
SPI Parameters
TxBD.addr
Tx Buffer
RBASE
ISB+0x89FC
TBASE
SPI_BASE
RFCR
TFCR
MRBLR
RSTATE
RBPTR
TSTATE
TBPTR
Figure 3. Example SPI BD and Buffer Memory Structure
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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7
Initialization Examples
4
Initialization Examples
This section gives examples of how to initialize I2C parameters, BD tables, and data buffers using the C
programming language.
4.1 Parameter RAM
Example 1 shows that the I2C parameter RAM table is implemented as a structure called t_I2c_Pram, with each
parameter being a structure member. The size of each parameter is specified by the following definitions:
•
VUBYTE is 8 bits
•
VUHWORD is 16 bits
•
VUWORD is 32 bits
Example 1. Setting up the I2C Parameter RAM Table
typedef struct
{
VUHWORD rbase;
VUHWORD tbase;
VUBYTE rfcr;
VUBYTE tfcr;
VUHWORD mrblr;
VUWORD rstate;
VUWORD rptr;
VUHWORD rbptr;
VUHWORD rcount;
VUWORD rtemp;
VUWORD tstate;
VUWORD tptr;
VUHWORD tbptr;
VUHWORD tcount;
VUWORD ttemp;
}t_I2c_Pram;
/*
/*
/*
/*
/*
/*
/*
/*
/*
/*
/*
/*
/*
/*
/*
RX
TX
Rx
Tx
Rx
Rx
Rx
Rx
Rx
Rx
Tx
Tx
Tx
Tx
Tx
BD base address */
BD base address */
function code */
function code */
buffer length */
internal state */
internal data pointer */
BD Pointer */
internal byte count */
temp */
internal state */
internal data pointer */
BD pointer */
byte count */
temp */
In this example, assume that the internal space base address is initialized to 0x14700000 and that the I2C parameter
table needs to be located at 0x14703800. Example 2 shows that I2CPRAM, which is a pointer to the I2C parameter
table structure t_I2c_Pram, is set to address 0x14703800. The I2C base address is configured as an array of two
bytes as shown in the last two lines in Example 2. The first and second arrays consist of the upper and lower bytes
of the I2C base address, respectively. These lines of code set the I2C base address to an offset of 0x3800 from the
dual-port RAM.
Example 2. Setting the I2C Parameter Table Location
t_I2c_Pram *I2CPRAM;
/* I2C Parameter RAM pointer */
I2CPRAM = (t_I2c_Pram *)(0x14703800);/* I2C Parameters base address */
IMM->pram.standard.i2c[0] = 0x38;
IMM->pram.standard.i2c[1] = 0x00;
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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RxBD Processing Example
4.2 Buffer Descriptors and Data Buffers
Example 3 shows that the BD table is implemented as a structure called BD, with each BD field being a
structure member. The BDRINGS structure allows for multiple RxBDs and TxBDs by implementing the BD
table as an array of BDs. For example, the first RxBD in the table is RxBD[0], the second is RxBD[1], and
the last RxBD in the table is RxBD[NUM_RXBDS-1].
Example 3. Setting up the Buffer Descriptor Tables
typedef struct BufferDescriptor
{
unsigned short cstat;
/* control and status*/
unsigned short length;
/* data length
char* addr;
/* buffer address
} BD;
*/
*/
typedef struct BufferDescRings
{
BD RxBD[NUM_RXBDS];
/* Rx BD ring */
BD TxBD[NUM_TXBDS];
/* Tx BD ring */
} BDRINGS;
In this example, assume that the RxBD and TxBD tables need to be located at the start of the dual-port RAM at
0x14700000. Example 4 shows that RxTxBD, which is a pointer to the BDRINGS structure, is set to point to
address 0x14700000. The last two lines of code set the parameters RBASE and TBASE to the start of the first
RxBD and the first TxBD in the tables, respectively.
Example 4. Setting the Buffer Descriptor Table Location
RxTxBD = (BDRINGS *)(0x1470000);
/* Pointer to BD area of DPRAM */
I2CPRAM->rbase = (UHWORD) & RxTxBD->RxBD[0]; /* point RBASE to first RX BD */
I2CPRAM->tbase = (UHWORD) & RxTxBD->TxBD[0]; /* point TBASE to first TX BD */
Example 5 shows how to set the first RxBD field values. Assume that rxbuf[0] is the buffer
referenced by RxBD[0]. This buffer can be placed in the dual-port RAM or in external memory.
Example 5. Setting the Buffer Descriptor Field Values
RxTxBD->RxBD[0].cstat = 0xB000;
RxTxBD->RxBD[0].length = 0;
RxTxBD->RxBD[0].addr = (char *) & rxbuf[0];
5
RxBD Processing Example
Figure 4 shows how the RxBD is processed in the SCC UART mode. This example assumes that the maximum
receive buffer length MRBLR is 8 bytes. The MRBLR is the number of bytes the MSC8101/MSC8103 writes to a
receive buffer before it moves to the next buffer. However, the MSC8101/MSC8103 can write fewer bytes than the
MRBLR value if an error or end-of-frame (for frame-based protocols) occurs. It never writes more bytes than the
MRBLR value, so the receive buffers cannot be smaller than the MRBLR.
When data arrives, the CP moves the data to the buffer to which the first RxBD in the table points. The CP
continues to move data until the buffer is full or an error occurs. When the buffer is full or an error occurs, the
buffer is closed. Subsequent data uses the next BD. If RxBD.cstat.E is cleared, the current buffer is not empty
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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9
RxBD Processing Example
and it reports a busy error. The CP does not move from the current BD until the SC140 core sets RxBD.cstat.E
to indicate that the buffer is empty. After using a descriptor, the CP clears RxBD.cstat.E and does not reuse a
BD until the SC140 core has processed it. However, in continuous mode when RxBD.cstat.CM is set,
RxBD.cstat.E remains set to allow the buffer to be overwritten when the CP accesses this BD again. When the
CP discovers a descriptor’s RxBD.cstat.W (wrap) is set, indicating that it is the last BD in the circular BD table,
it returns to the beginning of the table when it is time to move to the next BD.
When the UART receives idle characters (all ones), the channel begins counting consecutive idle characters
received. If the maximum idle characters MAX_IDL is reached, RxBD.cstat.ID is set, the buffer is closed and
an interrupt is generated if not masked.
When the UART receives no stop bit it reports framing errors. The channel writes the received character to the
buffer, closes it, sets RxBD.cstat.FR, generates an interrupt if not masked, and increments the received
characters with framing error counter FRMEC. A new receive buffer is used to receive subsequent data.
SCC UART RxBD.cstat
MRBLR = 8 Bytes
0
E
1
2
3
4
5
W
I
C
A
8000
Byte 1
xxxx
Byte 2
...
0001
2020
8000
RxBD 2
xxxx
Idle
Time-Out
0055
4750
8000
RxBD 3
xxxx
FF07
F000
RxBD n
8
CM ID AM
9
10
11 12 13 14
BR FR PR
15
OV CD
Clears RxBD.cstat.E after buffer is full (8 bytes received).
Writes 0x08 to RxBD.length.
Byte 1
Proceeds to next RxBD since RxBD.cstat.W=0.
Byte 2
Empty
Byte 1
Byte 4
Framing
Error
RxBD 1
Receives characters and stores in the buffer at 0x12020.
Byte 8
...
Byte 4
Error
RxBD 2
Receives characters and stores in the buffer at 0x554750.
Sets RxBD.cstat.ID because a programmable number
of consecutive idle sequences (MAX_IDL) was received.
Writes 0x02 to RxBD.length. (2 bytes received before
idle time-out occurred).
Proceeds to next RxBD since RxBD.cstat.W=0.
Empty
A000
Byte 1
xxxx
Byte 2
0089
C000
7
CPM Action:
RxBD Table
RxBD 1
6
...
RxBD 3
Receives characters and stores in the buffer at 0xFF07F000.
Sets RxBD.cstat.FR because byte 4 contains a frame
error.
Byte 8
Writes 0x04 to RxBD.length.
Proceeds to next RxBD since RxBD.cstat.W=0.
RxBD 4
Receives characters and stores in the buffer at 0x89C000.
Clears RxBD.cstat.E after buffer is full.
Proceeds to RxBD #1 since RxBD.cstat.W=1.
Figure 4. Example SCC UART RxBD Processing
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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TxBD Processing Example
6
TxBD Processing Example
Figure 5 shows how the TxBD is processed in the SCC UART mode. When the CP detects that the
TxBD.cstat.R (ready) is set, it starts transmitting the buffer. After the buffer is transmitted, the CP waits for the
next descriptor’s TxBD.cstat.R to be set before proceeding. When the CP detects that a descriptor’s
TxBD.cstat.W (wrap) is set, indicating this BD is the last in the BD table, it returns to the start of the BD table
after this last BD is processed. The CP clears TxBD.cstat.R (not ready) after using a TxBD, which keeps it
from being retransmitted before it is confirmed by the SC140 core. However, some protocols support a continuous
mode for which TxBD.cstat.R remains set after the buffer is closed to allow the buffer to be resent next time
the CP accesses this BD. Continuous mode is enabled by setting TxBD.cstat.CM.
SCC UART TxBD.cstat
0
1
R
2
3
W
I
4
CR A
8000
TxBD.length
0027
TxBD.addr
0001
2020
9000
TxBD 1
TxBD 2
10
11 12
13 14
NS
15
CT
TxBD 1
Transmits 0x27 characters from the buffer
at 0x12020.
Proceeds to next TxBD since TxBD.cstat.W = 0.
Sets SCCE[TX] after buffer is processed by the CP, which
can cause an interrupt since TxBD.cstat.I=1.
Proceeds to next TxBD since TxBD.cstat.W = 0.
FF07
F000
.
.
.
0089
C000
9
Clears TxBD.cstat.R after buffer is sent.
TxBD 3
0035
0018
CM P
8
TxBD 2
Transmits 0x104 characters from the buffer
at 0x554750.
0055
4750
A000
7
Clears TxBD.cstat.R after buffer is sent.
0104
8200
6
CPM Action:
TxBD Table
TxBD.cstat
5
TxBD n
TxBD 3
Transmits 0x35 characters from the buffer
at 0xFF07F000.
TxBD.cstat.R remains set since TxBD.cstat.CM = 1.
Proceeds to next TxBD since TxBD.cstat.W = 0.
TxBD n
Transmits 0x18 characters from the buffer
at 0x89C000.
Clears TxBD.cstat.R after buffer is sent.
Proceeds to TxBD 1 since TxBD.cstat.W = 1.
Figure 5. Example SCC UART TxBD Processing
Initializing MSC8101/MSC8103 CPM Parameter RAM and Buffer Descriptors, Rev. 2
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11
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AN2147
Rev. 2
11/2004
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