Re: SmartPort Question

[dempson@actrix.gen.nz (David Empson)]

Bryan Parkoff <BParkoff@satx.rr.com> wrote:

>     I learn that Apple IIgs Reference book says that SmartPort will support
> printer, modem, network, etc near the future, but it does not exist.

As David Wilson noted in another followup, the term "SmartPort" has two
distinct meanings:

- The protocol used to communicate via the disk port with intelligent
devices like the UniDisk 3.5.

- The firmware interface provided by many 3.5" drive controller cards,
Apple SCSI cards, standard slot RAM cards, and the built-in SmartPort
firmware of the Apple IIc and IIgs (slot 5).

The protocol and the firmware interface support both block and character
devices, but all the implementations I can think of have been block
devices.

>     It also says that it can support up to 127 SmartPort devices.

In theory, yes.  The SmartPort protocol uses a 7-bit field in the packet
header to identify the peripheral (with a value of zero being reserved),
and the firmware interface uses the same convention.

Specific implementations of the SmartPort firmware interface have lower
limits on the actual number of devices.  For example, the original Apple
SCSI card only supports 7 devices, and the Apple High-speed SCSI card
supports 110 (to achieve this, you would need a lot of hard drives, each
with several partitions).

The actual disk ports have a much lower limit, due to signal loading and
power supply restrictions.  I wouldn't recommend trying to connect more
than four drives to a single disk port.

> I suspect that it can only limit to 14 devices under ProDOS 8 because it
> uses slot 1 through 7.

If you use ProDOS-8 2.0.1 or later, ProDOS can make use of the SmartPort
firmware interface and can remap SmartPort units into unused ProDOS unit
numbers.  You are limited to a maximum of 13 units (S3,D2 is reserved
for /RAM), and each slot occupied by another disk controller card (or a
device which look like one) will reduce the number of remappable units
by two.

This only affects accessing the SmartPort devices via ProDOS.
Application code can use the SmartPort firmware interface directly, and
bypass the limits imposed by ProDOS.

> If it is true that ProDOS 16 supports up to 16 devices per slot.

Nope.  ProDOS-16 supports two devices per slot, like early versions of
ProDOS-8.  ProDOS-16 has no support for the SmartPort firmware interface
(it only uses the ProDOS block driver in the card's firmware).

GS/OS has a more powerful driver architecture, supporting a mixture of
"loaded" drivers (supplied as files on the system disk) and "generated"
drivers (which make use of the firmware supplied by the I/O card).

For a card which supports the SmartPort firmware interface, GS/OS can
generate a driver for each block device (and theoretically for each
character device).  It may be possible to reach the SmartPort limit of
127 devices given the right setup.

This is somewhat of a moot point, since GS/OS requires the use of loaded
drivers for most of the common SmartPort peripherals (Apple 3.5 Drive,
UniDisk 3.5 and Apple SCSI).

-- 
David Empson
dempson@actrix.gen.nz