TDM Basics
MSC8113 Reference Manual, Rev. 0
Freescale Semiconductor
20-23
occupying double the size. The A/
μ
-law conversion is performed according to the ITU-T
recommendation G.711.
Note:
The minimum buffer size for both transmit and receive is 16 bytes (that is, the
RDBS/TDBS value is 0x00000F). The maximum buffer size for both transmit and
receive is 16 MB (that is, the RDBS/TDBS value is 0xFFFFFF), but it can be further
limited by the main memory size according to the number of channels in the frame.
Figure 20-24 shows how the samples are stored in the receive main data buffer (if the receive
channel is A/
μ
law) or the transmit main data buffer (if the transmit channel is A/
μ
law).
20.2.6.2 Data Buffer Address
The address of a receive buffer is a function of the following:
Receive Global Base Address. TDMxRGBA[RGBA], page 20-52.
Receive Channel Data Base Address. TDMxRCPRn[RCDBA] field, page 20-58. RGBA
<< 16 + RCDBA points to the first byte of receive data buffer n. The four lsbs of RCDBA
must be 0000.
Receive Data Buffer Displacement. TDMxRDBDR[RDBD] field, page 20-62. Adding this
field to the first byte of receive data buffer n indicates the location to which the TDM will
write next: RGBA << 16 + RCDBA + RDBD is the current write pointer to the receive
data buffer n. In most cases, the RDBD can be used to indicate that data is written to the
buffer and can be processed. However, in some cases in which the local bus is extremely
busy and the TDM priority is low, the pointer may be updated before the data is actually to
the internal memory. This typically affects the last channel transmitted. In all cases, when
configured to reflect the last buffer configuration, assertion of the receive buffer threshold
interrupt indicates that the data was updated in memory.
The address of a transmit buffer is a function of the following:
Transmit Global Base Address. TDMxTGBA[TGBA] field, page 20-52
Transmit Channel Data Base Address. TDMxTCPRn[TCDBA] field, page 20-59. TGBA
<< 16 + TCDBA points to the first byte of transmit data buffer n. The four lsbs of TCDBA
must be 0000.
Figure 20-24. Receive/Transmit Main Data Buffer For A-Law/
μ
-Law Channel
smp #4
smp #5
smp #6
smp #7
smp #0
smp #1
smp #2
smp #3
smp #C
smp #D
smp #E
smp #F
smp #8
smp #9
smp #A
smp #B
16 bit
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