Specifications

System Macros Invoked by Drivers
SPI$SET_CONNECTION_CHAR
SPI$SET_CONNECTION_CHAR
Sets characteristics of an existing connection.
Format
SPI$SET_CONNECTION_CHAR
Description
The SPI$SET_CONNECTION_CHAR macro sets characteristics of an existing
SCSI connection. Prior to altering the characteristics of a connection, a SCSI
class driver should read and examine the current connection characteristics using
the SPI$GET_CONNECTION_CHAR macro.
The class driver specifies the characteristics to be set for the connection in a
connection characteristics buffer. The buffer has the format listed in Table 2–12.
Table 2–12 SPI$SET_CONNECTION_CHAR Macro Settable Characteristics
Longword Contents
1 Number of longwords in the buffer, not including this
longword. The value of this field must be 10.
2 Connection flags. Bits in this longword are defined as follows:
Bit Description
0 ENA_DISCON. When set, this bit enables disconnect
and reselection on the connection.
1 DIS_RETRY. When set, this bit disables command
retry on the connection.
3 Synchronous. When this longword contains 0, the connection
uses asynchronous data transfer mode; when it contains a
nonzero value, the connection uses synchronous data transfer
mode.
4 Transfer period. If the synchronous parameter is nonzero,
this field controls the number of 4-nanosecond ticks between
a REQ and an ACK. The default is 64
10
.
5 REQ-ACK offset. If the synchronous parameter is nonzero,
this field controls the maximum number of REQs outstanding
before there must be an ACK.
6 Busy retry count. Maximum number of retries allowed on
this connection while waiting for the port to become free.
7 Arbitration retry count. Maximum number of retries
allowed on this connection while waiting for the port to
win arbitration of the bus.
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