DMA Controller
Am186™CC/CH/CU Microcontrollers User’s Manual
8-27
performs this operation without software intervention, the latency is significantly lower than
if an interrupt task performed the same operation.
Software must still read and write the buffer descriptors, but the latency requirements are
greatly relaxed because multiple descriptors are queued at one time. The software can
take, on average, the time it takes to transmit or receive a buffer to update each descriptor,
and software can increase allowable latency even more by updating several descriptors at
the same time.
8.5.7.2
SmartDMA Channel Request Source and Synchronization
The SmartDMA channels support only specific, predetermined request sources. These
sources in turn determine the synchronization type for each channel. Synchronization type
for the SmartDMA channels is not programmable. The synchronization types are shown in
Table 8-10, Table 8-11, and Table 8-12.
The memory buffer addresses are taken from the buffer descriptor ring, as explained in
“SmartDMA Channel Memory Overview” on page 8-28.
In the Am186CC microcontroller, SmartDMA Channel 2 and SmartDMA Channel 3 provide
the DSEL bit in the SDxCON control register for selecting between the HDLC and USB
request source. The address of the peripheral does not need to be programmed into the
SmartDMA channel because these devices have an internal interface to the associated
SmartDMA channel.
In the Am186CU USB microcontroller, the DSEL bit must be programmed correctly for USB
support.
The SmartDMA channels support only byte transfers. The data is written or read from
sequential byte addresses in the memory buffers.
Table 8-10
Am186CC SmartDMA Channel Request Source and Synchronization
SmartDMA
Channel
Direction Source
Destination
Synchronization
0
Transmit
Memory buffer
HDLC A transmit FIFO
Destination
Receive
HDLC A receive FIFO
Memory buffer
Source
1
Transmit
Memory buffer
HDLC B transmit FIFO
Destination
Receive
HDLC B receive FIFO
Memory buffer
Source
2
Transmit
Memory buffer
HDLC C transmit FIFO or
USB endpoint B transmit
FIFO
Destination
Receive
HDLC C receive FIFO or
USB endpoint A receive FIFO
Memory buffer
Source
3
Transmit
Memory buffer
HDLC D transmit FIFO or
USB endpoint D transmit
FIFO
Destination
Receive
HDLC D receive FIFO or
USB endpoint C receive FIFO
Memory buffer
Source
CC
CU
CC
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...