Printer Using Direct Memory Access to Reduce Communications Bandwidth
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Jordan, DD: AUTHOR [+5]
Disclosed is a system for reducing the processor bandwidth required to accept inbound data communications. This system uses a combination of Direct Memory Access (DMA), custom hardware and control software.
Printer Using Direct Memory Access to Reduce Communications BandWidth
a system for reducing the processor
bandwidth required to accept inbound data communications. This
system uses a combination of Direct Memory Access (DMA), custom
hardware and control software.
handle the processing of inbound data via
dedicated interrupt service routines. Each time a new inbound byte
is received, the interrupt routine is executed. The data is moved
from an I/O port into a data buffer. Significant processor bandwidth
is required to perform this task.
describes a system that employs DMA, custom
hardware and control software to perform inbound data communications
at greatly reduced processor bandwidth requirements. A block diagram
containing a high-level schematic of the data communications design
is given in the figure.
communications are performed as follows:
1. The host sends an input data byte to the printer.
Printer hardware places the byte in the parallel
communications port, asserts a BUSY signal to the
host, and asserts a DMA request to the printer
2. The printer DMA hardware places a copy of the
input data into the input buffer. Parsing of the
input buffer is performed in the usual manner.
3. As soon as the DMA hardware reads the
communications port, the printer hardware negates
the BUSY signal.
4. The input buffer parser is responsible for moving
data out of the input buffer. Depending on the
size of the buffer, the speed of the parser, and
the inbound data rate, it may be possible to fill
the buffer. If the parser sees that the buffer is
becoming full, the parser will instruct the
printer hardware to assert a BUSY si...