using the bootstrap loader

5.2 DEVICE INITIALIZE PROCEDURE
WRITING A CUSTOM FIRST-STAGE DRIVER
The device initialize procedure must present the following PL/M-86 interface to the
Bootstrap Loader:
device$init: PROCEDURE (unit) WORD PUBLIC;
DECLARE unit WORD;
END device$init;
where:
(code as described below)
device$init The name of the device initialize procedure. You can choose any name
you wish for this procedure, as long as it does not conflict with the
names of any other first-stage procedure.
unit The device unit number, as defined during Bootstrap Loader
configuration.
The WORD value returned by the procedure must be the device granularity (fu bytes) if
the device is ready, or zero if the device is not ready.
To be compatible with the Bootstrap Loader, the device initialize procedure must do the
following steps:
1. Test to see if the device is present. If not, return the value zero.
2. Initialize the device for reading. This operation is device-dependent. For guidance in
initializing the device, refer to the hardware reference manual for the device.
3. Test to see if device initialization is successful. If not, return the value zero.
4. Obtain the device granularity. For some devices, only one granularity is possible,
while for other devices several granularities are possible. The hardware reference
manual for your device explains this device-dependent issue.
5. Return the device granularity.
NOTE
Besides the above five steps, the procedure must follow MUL TIBUS II
transport protocol and belong to the BSL-Drivers COMPACT sub-system if the
driver functions in a non-MSA MULTIBUS II environment. Refer to Section
5.5 for more information on these two requirements.
Bootstrap Loader 5-3