ADSP-2181
When the BWCOUNT register is written with a nonzero value,
the BDMA circuit starts executing byte memory accesses with
wait states set by BMWAIT. These accesses continue until the
count reaches zero. When enough accesses have occurred to
create a destination word, it is transferred to or from on-chip
memory. The transfer takes one DSP cycle. DSP accesses to
external memory have priority over BDMA byte memory ac-
cesses.
The BDMA Context Reset bit (BCR) controls whether the
processor is held off while the BDMA accesses are occurring.
Setting the BCR bit to 0 allows the processor to continue opera-
tions. Setting the BCR bit to 1 causes the processor to stop
execution while the BDMA accesses are occurring, to clear the
context of the processor and start execution at address 0 when
the BDMA accesses have completed.
Internal Memory DMA Port (IDMA Port)
Table VI. Boot Summary Table
MMAP
0
BMODE
0
Booting Method
BDMA feature is used in default mode
to load the first 32 program memory
words from the byte memory space.
Program execution is held off until all
32 words have been loaded.
IDMA feature is used to load any inter-
nal memory as desired. Program execu-
tion is held off until internal program
memory location 0 is written to.
Bootstrap features disabled. Program
execution immediately starts from
location 0.
0
1
1
X
The IDMA Port provides an efficient means of communication
between a host system and the ADSP-2181. The port is used to
access the on-chip program memory and data memory of the
DSP with only one DSP cycle per word overhead. The IDMA
port cannot, however, be used to write to the DSP’s memory-
mapped control registers.
The IDMA port has a 16-bit multiplexed address and data bus
and supports 24-bit program memory. The IDMA port is
completely asynchronous and can be written to while the
ADSP-2181 is operating at full speed.
The DSP memory address is latched and then automatically
incremented after each IDMA transaction. An external device
can therefore access a block of sequentially addressed memory
by specifying only the starting address of the block. This in-
creases throughput as the address does not have to be sent for
each memory access.
IDMA Port access occurs in two phases. The first is the IDMA
Address Latch cycle. When the acknowledge is asserted, a 14-
bit address and 1-bit destination type can be driven onto the bus
by an external device. The address specifies an on-chip memory
location; the destination type specifies whether it is a DM or
PM access. The falling edge of the address latch signal latches
this value into the IDMAA register.
Once the address is stored, data can either be read from or
written to the ADSP-2181’s on-chip memory. Asserting the
select line (IS) and the appropriate read or write line (IRD and
IWR
respectively) signals the ADSP-2181 that a particular
transaction is required. In either case, there is a one-processor-
cycle delay for synchronization. The memory access consumes
one additional processor cycle.
Once an access has occurred, the latched address is automati-
cally incremented and another access can occur.
Through the IDMAA register, the DSP can also specify the
starting address and data format for DMA operation.
Bootstrap Loading (Booting)
BDMA Booting
When the BMODE and MMAP pins specify BDMA booting
(MMAP = 0, BMODE = 0), the ADSP-2181 initiates a BDMA
boot sequence when reset is released. The BDMA interface is
set up during reset to the following defaults when BDMA boot-
ing is specified: the BDIR, BMPAGE, BIAD and BEAD regis-
ters are set to 0, the BTYPE register is set to 0 to specify
program memory 24 bit words, and the BWCOUNT register is
set to 32. This causes 32 words of on-chip program memory to
be loaded from byte memory. These 32 words are used to set up
the BDMA to load in the remaining program code. The BCR
bit is also set to 1, which causes program execution to be held
off until all 32 words are loaded into on-chip program memory.
Execution then begins at address 0.
The ADSP-2100 Family Development Software (Revision 5.02
and later) fully supports the BDMA booting feature and can
generate byte memory space compatible boot code.
The IDLE instruction can also be used to allow the processor to
hold off execution while booting continues through the BDMA
interface.
IDMA Booting
The ADSP-2181 can also boot programs through its Internal
DMA port. If BMODE = 1 and MMAP = 0, the ADSP-2181
boots from the IDMA port. IDMA feature can load as much on-
chip memory as desired. Program execution is held off until on-
chip program memory location 0 is written to.
The ADSP-2100 Family Development Software (Revision 5.02
and later) can generate IDMA compatible boot code.
Bus Request and Bus Grant
The ADSP-2181 can relinquish control of the data and address
buses to an external device. When the external device requires
access to memory, it asserts the bus request (BR) signal. If the
ADSP-2181 is not performing an external memory access, then
it responds to the active
BR
input in the following processor
cycle by:
• three-stating the data and address buses and the
PMS, DMS,
BMS, CMS, IOMS, RD, WR
output drivers,
• asserting the bus grant (BG) signal, and
• halting program execution.
The ADSP-2181 has two mechanisms to allow automatic load-
ing of the on-chip program memory after reset. The method for
booting after reset is controlled by the MMAP and BMODE
pins as shown in Table VI.
REV. D
–9–
AD [ ANALOG DEVICES ]
