Table of Contents
Advertisement
I/O Handling
143
BASIC statements also obtain and release access as I/O is performed. The following table lists
some of the ways access is used by the system:
Use
Access
Cartridge Operations
SYNC (HIGH select code)
Flexible Disk Operations
DMA
PRINT, PRINT USING
ASYNC
Plotter Drivers
ASYNC
CARD ENABLE
ASYNC
ENTER/ OUTPUT INT
ASYNC
ENTER/OUTPUT DMA
DMA
ENTER / OUTPUT FHS
1
DMA
In general, single BASIC statements could cause access to be granted and released several
times. For example, the cartridge operations obtain and release synchronous access once for
each physical record transferred.
UTILITY:
Isr access
This utility is used to request access and, if the access is granted, to create the linkage between
an interrupt service routine (lSR) and a select code. Pressing RESET (
(CONnll
STOP
I)
during execu-
tion of the utility may cause a SCRATCH A to be issued.
General Procedure: The utility is told where the ISR resides and what kind of access is
required. If access is granted, it re,turns successfully. If access is not granted immediately, it
keeps trying periodically until it is successful or until a specified number of attempts have been
made (in which case
it
returns unsuccessfully).
Special Requirements: The B register must contain information as follows -
Bits
Description
0-3
Select code to be linked to the ISR
4-5
Access code (see next page)
8 -14 Number of attempts to be made before aborting
1 In addition to obtaining DMA acces; (which in this case is used just to ensure there is no synchronous access granted), the FHS
drivers disable all interrupts during the actual transfer loop.
Advertisement
Table of Contents
