Computer Hardware User's Guide

DMA Controller
12-77 Peripherals
Example 12–10 sets up the DMA to transfer data (128 words) from an array
buffer to the serial port 0 output register with serial port transmit interrupt XINT0.
The DMA sends an interrupt to the CPU when the data transfer completes.
Serial port 0 is initialized to transmit 32-bit data words with an internally gener-
ated frame sync and a bit-transfer rate of 8(H1) cycles/bit. The receive-bit
clock is internally generated and equal in frequency to one-half of the ’C3x H1
frequency.
This program assumes previous initialization of the CPU interrupt-vector table
(specifically the DMA-to-CPU interrupt). The serial-port interrupt directly affects
only the DMA; no CPU serial-port interrupt-vector setting is required.
Note: Serial-Port Transmit Synchronization
The DMA uses serial-port transmit interrupt XINT0 to synchronize transfers.
Because the XINT0 is generated when the transmit buffer has written the last
bit of data to the shifter, an initial CPU write to the serial port is required to
trigger XINT0 to enable the first DMA transfer.
Example 12–10. DMA Transfer With Serial-Port Transmit Interrupt
* TITLE: DMA TRANSFER WITH SERIAL PORT TRANSMIT INTERRUPT
* .GLOBAL START
.DATA
DMA .WORD 808000H ; DMA GLOBAL-CONTROL REG ADDRESS
CONTROL .WORD 0E13H ; DMA GLOBAL-CONTROL REG INITIALIZATION
SOURCE .WORD (_ARRAY+1) ; DATA SOURCE ADDRESS
DESTIN .WORD 80804CH ; DATA DESTIN ADDRESS: SERIAL-PORT OUTPUT REG
COUNT .WORD 127 ; NUMBER OF WORDS TO TRANSFER =(MSG LENGHT–1)
IEVAL .WORD 00100400H ; IE REGISTER VALUE
.BSS _ARRAY,128 ; DATA ARRAY LOCATED IN .BSS SECTION
; THE UNDERSCORE USED IS JUST TO MAKE IT
; ACCESSIBLE FROM C (OPTIONAL)
RESET1 .WORD 0E10H ; DMA RESET
SPORT .WORD 808040H ; SERIAL-PORT GLOBAL–CONTROL REG ADDRESS
SGCCTRL .WORD 048C0044H ; SERIAL-PORT GLOBAL-CONTROL REG INITIALIZATION
SXCTRL .WORD 111H ; SERIAL-PORT TX PORT CONTROL REG INITIALIZATION
STCTRL .WORD 00FH ; SERIAL-PORT TIMER CONTROL REG INITIALIZATION
STPERIOD .WORD 00000002H ; SERIAL-PORT TIMER PERIOD
SPRESET .WORD 00880044H ; SERIAL-PORT RESET
RESET .WORD 0H ; SERIAL-PORT TIMER RESET
.TEXT
START LDP DMA ; LOAD DATA PAGE POINTER