IDMA Channels
MOTOROLA
MC68360 USER’S MANUAL
7-37
W—Wrap (Final BD in Table)
0 = This is not the last BD in the table.
1 = This is the last BD in the table. After the associated buffer has been used, the RISC
controller will transfer data from the first BD in the table (pointed to by IBASE). The
number of BDs in this table is programmable and is determined only by the W-bit
and the overall space constraints of the dual-port RAM.
I—Interrupt
0 = No interrupt is generated after this buffer has been serviced.
1 = When this buffer has been serviced by the RISC controller the AD bit in the CSR
will be set, which can cause an interrupt.
L—Last
0 = This is not the last buffer to be transferred in the buffer chaining mode. The I-bit
may be used to generate an interrupt when this buffer has been serviced.
1 = This is the last buffer to be transferred in the buffer chaining mode. When the trans-
fer count is exhausted, the START bit will be reset and an interrupt (DONE) will be
generated, regardless of the I-bit.
CM—Continuous Mode
0 = Buffer chaining mode. The RISC will clear the V-bit after this BD is serviced. The
buffer chaining mode is used for transferring large quantities of data into noncon-
tiguous buffer areas. The user can initialize BDs ahead of time, if desired. The
RISC controller automatically reloads the IDMA registers from the next BD’s values
when the transfer is terminated. If DONEx is asserted by an external peripheral,
the buffer will be closed, the STR bit will be reset, and the DONE bit will be set in
the CSR, which can cause an interrupt.
1 = Auto buffer mode (continuous mode). The RISC will not clear the V-bit after this BD
is serviced. This is the only difference between auto buffer mode and buffer chain-
ing mode behavior. The auto buffer mode is used to transfer multiple groups of data
to/from a buffer ring. This mode does not require reprogramming. The RISC con-
troller automatically reloads the IDMA registers from the next BD values when the
transfer is terminated. Either a single BD or multiple BDs may be used in this mode
to create an infinite loop of repeated data moves.
NOTE
The I-bit may still be used to generate an interrupt in this mode.
The following bits are written by the RISC controller after it has finished receiving data from
the associated data buffer.
SE—Source Access Bus Error
The buffer was closed due to a bus error on the source access. An interrupt (BES) will be
generated, regardless of the I-bit. The RISC will clear the V-bit of this BD.