DMA Controller
8-10
Am186™CC/CH/CU Microcontrollers User’s Manual
the CPU to respond quickly to the NMI request. Software can also inhibit DMA transfers by
setting the DHLT bit in the DMAHLT register.
Priorities for the general-purpose DMA channels are set through the GDxCON0 registers;
SmartDMA channel priorities are set with the SDxCON registers.
8.5.3
DMA Request Synchronization
Synchronized data transfers are either source or destination synchronized—either the
source of the data or the destination of the data generates a DRQ to request the data
transfer. Note that the terms source and destination are relative to the data movement. For
example, a UART receiver is source-synchronized; the UART is the source of the data and
the DRQ (see Figure 8-2).
DMA transfers can also be unsynchronized (i.e., DRQ is always asserted, and the transfer
takes place continually until the correct number of transfers has occurred).
For more information about general-purpose DMA channel synchronization, see “Setting
Synchronization” on page 8-17. For more information about SmartDMA channel
synchronization, see “SmartDMA Channel Request Source and Synchronization” on
page 8-27.
Figure 8-2
Source Versus Destination Synchronization
8.5.4
DMA Acknowledge
The Am186CC/CH/CU microcontrollers do not provide an explicit DMA acknowledge signal.
Because both source and destination registers are maintained, a read from a requesting
source or a write to a requesting destination serves as the DMA acknowledge signal.
Because the chip-select lines can be programmed to be active for a given block of memory
or I/O space, and the DMA source and destination address registers can point to the same
given block, a chip-select line can indicate a DMA acknowledge.
8.5.5
DMA and Interrupts
In some cases, a combination of both DMA processing and interrupt processing is
appropriate (e.g., when a certain amount of protocol processing must be performed for
each character, and this processing should take place at the interrupt level). In this situation,
using a circular receive buffer with extended reads can effectively extend or replace the
UART FIFO with a buffer in main memory. For more information, see “Using Buffer Queues
Serial Port Receive Data
Serial Port Transmit Data
(SPRXD) Register
(SPTXD) Register
RXD
TXD
Memory Buffer
UART Receiver
UART Transmitter
Here the source of the data is requesting
the transfer so the UART Receiver is
source-synchronized.
Here the destination of the data is requesting
the transfer so the UART Transmitter is
destination synchronized.
Содержание Am186 CC
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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...