DMA Controller
Am186™CC/CH/CU Microcontrollers User’s Manual
8-35
In the Am186CU USB microcontroller, the DSEL bit in the SDxCON register must be
set to 1.
Software clears the status bits in SDxSTAT after receiving an interrupt. Software can use
the SDxCBD register to monitor the transmit and receive buffers. Software can also use
the SDxCRAD register to determine the address in memory where the DMA receive process
was interrupted.
Enable the Receive Channel
Enable the receive channel by setting the RXST bit in the SDxCON register to 1.
At this point, the SmartDMA receive channel is enabled. As received data is processed,
software should modify entries in the ring to point to empty data buffers. Buffers are added
to the ring at the first ring location following the Current Buffer Descriptor value that has an
OWN bit cleared to 0.
Replace Used Data Buffers
1. Program the new data buffer address.
a. Program the LADR bits in Word 0 to the low-order 16 address bits of the data buffer
pointed to by the descriptor.
b. Program the HADR bits in Word 1 to the high-order eight address bits of the data
buffer pointed to by the descriptor. The highest four bits of the address must be set to
0000b. These address bits do not exist on the Am186CC/CH/CU microcontrollers’
20-bit address but are provided for LANCE compatibility.
2. Set to 1 the OWN bit in Word 1 to indicate the descriptor entry is owned by the SmartDMA
channel.
3. To force a poll of the OWN bit of the current buffer descriptor, set to 1 the POLL bit in
the SDxCON register. This bit has no effect if the SmartDMA channel is not currently
waiting for a buffer to become available.
8.5.7.4.3
Enable the Peripheral Device
Details for configuring and enabling the HDLC peripheral device being used can be found
in Chapter 15, “High-Level Data Link Control (HDLC).”
Details for configuring and enabling the USB peripheral device being used can be found in
Chapter 18, “Universal Serial Bus (USB).”
The DMA should always be enabled before the requesting device is enabled. The DMA
should always be disabled after the requesting device is disabled.
8.5.7.5
SmartDMA Channel Cycle
This section and the following sections describe the procedure the SmartDMA controller
follows for both a transmit and a receive.
8.5.7.5.1
SmartDMA Transmit Channel Cycle
The flow diagram for the SmartDMA transmit channel is shown graphically in Figure 8-8 on
page 8-37 and discussed below.
1. When the transmit channel is first enabled, the SmartDMA controller enters initialization
mode.
2. The transmit channel reads the current descriptor and checks to see if the owner
semaphore (OWN) bit is set to 1.
CU
CC
CH
CC
CU
Summary of Contents for Am186 CC
Page 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Page 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Page 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Page 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Page 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Page 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Page 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Page 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Page 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...