Support IOC commands for disk/drum devices

Thanks to Kevin Brunelle

There is a minor fix included with regards to tape devices. The test
was failing if M == 0, when it should fail when M != 0.

NOTICE: This patch changes the behavior of the VM and changes the
function parameters for the ioc_ function. Documentation changes are
included.

Permits the following:
     LDX   BLKNUM
     IOC   0(8)
     OUT   ADDR(8)      Write block from ADDR into disk[BLKNUM]
     IOC   0(8)
     IN    ADDR(8)      Read block from disk[BLKNUM] into ADDR
...
BLKNUM  CON  45000      Example possible block on disk

I was having an issue writing a block to a drive and then reading back
the same block. Because it is impossible to move the SEEK_CUR pointer
backwards on a disk device, there was no way for a program to read
back a block that it wrote to a disk without restarting or fiddling
with ~/.mdk/disk?.dev files and symbolic links.

I have added a function parameter to the ioc_ function and used it to
pass the value of rX to ioc_. This permits us to use IOC commands to
move the read/write head on a disk/drum device. I believe that this
conforms to the potential meaning of Knuth's description of IOC for
disk/drum devices.

I have put in tests to verify that rX is positive and M = 0.

I have updated the documentation to reflect this new behavior.

This makes disks much more usable.

Note: I won't be offended if this patch is rejected because it changed
the behavior of the VM. I think it fits the spirit and enhances the
functionality in a way that some might find useful. I wanted it for
something I was working on, and I felt others might want the same. The
thing with the paper-tape should be fixed, though.

0 files changed, 0 insertions, 0 deletions