DMA Controller
Am186™CC/CH/CU Microcontrollers User’s Manual
8-33
d. Set to 1 the OWN bit in Word 1 to indicate the descriptor entry is owned by the
SmartDMA channel.
e. To force a poll of the OWN bit of the current buffer descriptor, set to 1 the POLL bit in
the SDxCON register. This has no effect if the SmartDMA is not currently waiting for
a buffer to become available.
5. In the Am186CC microcontroller, when using SmartDMA channel 2 or 3, select one of
two alternate sources by clearing the DSEL bit in the SDxCON register to 0 to select
HDLC or to 1 to select USB.
In the Am186CH HDLC microcontroller, the DSEL bit in the SDxCON register must be
cleared to 0.
In the Am186CU USB microcontroller, the DSEL bit in the SDxCON register must be
set to 1.
Enable the Transmit Channel
Enable the transmit channel by setting the TXST bit in the SDxCON register to 1. At this
point, the SmartDMA transmit channel does not transmit any data because there are no
valid buffers in the descriptor ring. As transmit data becomes available, software should
modify entries in the ring to point to the data to be transmitted. Buffers are added to the
ring at the first ring location following the Current Transmit Buffer Descriptor value that has
an OWN bit set to 0.
8.5.7.4.2
Enabling the Receive Channel
To enable a SmartDMA receive channel, software must perform the following tasks:
1. Create the receive buffer descriptor ring.
2. Program the interrupt channel and configure the SmartDMA channel for interrupts.
3. Add data buffers to the ring.
4. Enable the receive channel.
5. Replace used data buffers.
Create the Receive Buffer Descriptor Ring
1. Disable the receive channel by clearing the RXST bit in the SDxCON register to 0.
2. Allocate the memory for the receive buffer descriptor ring (see “SmartDMA Channel
Descriptor Format” on page 8-38 for the descriptor ring data structure).
3. Set the OWN bit for each descriptor to 1 (owned by hardware).
4. Program the address and size of the receive buffer descriptor ring into the SmartDMA
channel registers.
a. Program the RRA bits in the SDxRRCAL register to the 12 low address bits
(bits 15–4) of the descriptor ring address, which is the start location in memory of the
buffer descriptor ring.
b. Program the RRA bits in the SDxRRAH register to the four high address bits (19–16)
of the descriptor ring address. Because the base address of the ring must be paragraph
aligned (aligned to a 16-byte physical memory boundary), address bits 3–0 are always
zeroes.
c. Program the RRC bits in the SDxRRCAL register to the number of entries in the receive
descriptor ring (the ring count). Valid values are 1, 2, 4, 8, 16, 32, 64, or 128 descriptors.
For information about 3-bit encoding, see the
Am186™CC/CH/CU Microcontrollers
CC
CH
CU
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...