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GP DMA Controller Registers
élanSC520 Microcontroller Register Set Manual
11-25
Buffer Chaining Valid (GPDMABCVAL)
Memory-Mapped
MMCR Offset D9Bh
Register Description
This register provides the operating interface with the buffer chaining feature.
Bit Definitions
Programming Notes
A channel’s CHx_CBUF_VAL bit is ignored if buffer chaining is not enabled for the channel. Buffer chaining is enabled
separately for each channel in the GPDMABCCTL register (see page 11-21).
If buffer chaining is enabled for a channel, and if the channel’s CHx_CBUF_VAL bit is set when the end of the buffer
is reached (i.e., when the channel’s Transfer Count register reaches 0), then the channel’s Memory Address and
Transfer Count registers are loaded with the values in the channel’s Next Address and Next Count registers,
respectively. Then the channel’s CHx_CBUF_VAL bit is cleared by the GP bus DMA controller. An interrupt is also
generated if the CHx_INT_ENB bit is set in the GPDMABSINTENB register (see page 11-24).
If buffer chaining is enabled and software has not set the channel’s CHx_CBUF_VAL bit before the end of the buffer
is reached, then the GPTC signal is asserted.
Note that software can only set the CHx_CBUF_VAL bit to indicate to the hardware that the Next Address and
Transfer Count registers contain valid information. The CHx_CBUF_VAL bit can be cleared only by hardware.
7
6
5
4
3
2
1
0
Bit
Reserved
CH7_
CBUF_VAL
CH6_
CBUF_VAL
CH5_
CBUF_VAL
CH3_
CBUF_VAL
Reset
0
0
0
0
0
0
0
0
R/W
RSV
R/W!
R/W!
R/W!
R/W!
Bit
Name
Function
7
–
4
Reserved
Reserved
This bit field should be written to 0 for normal system operation.
3
CH7_CBUF_
VAL
Chaining Buffer Valid for Channel 7
0 =
The channel’s Next Address registers and Next Transfer Count registers are not valid.
Only hardware can clear this bit. Writing a 0 has no effect.
1 =Software sets this bit to indicate that the values of the channel’s Next Address registers
and Next Transfer Count registers are valid.
2
CH6_CBUF_
VAL
Chaining Buffer Valid for Channel 6
0 =The channel’s Next Address registers and Next Transfer Count registers are not valid.
Only hardware can clear this bit. Writing a 0 has no effect.
1 =Software sets this bit to indicate that the values of the channel’s Next Address registers
and Next Transfer Count registers are valid.
1
CH5_CBUF_
VAL
Chaining Buffer Valid for Channel 5
0 =The channel’s Next Address registers and Next Transfer Count registers are not valid.
Only hardware can clear this bit. Writing a 0 has no effect.
1 =Software sets this bit to indicate that the values of the channel’s Next Address registers
and Next Transfer Count registers are valid.
0
CH3_CBUF_
VAL
Chaining Buffer Valid for Channel 3
0 =The channel’s Next Address registers and Next Transfer Count registers are not valid.
Only hardware can clear this bit. Writing a 0 has no effect.
1 =Software sets this bit to indicate that the values of the channel’s Next Address registers
and Next Transfer Count registers are valid.