[Simh] something strange with simulated RK05 drive ?

[Paul Koning]

> On Feb 11, 2020, at 3:15 PM, Henk Gooijen <henk.gooijen at hotmail.com> wrote:
> 
> I am building a replica RK05 disk drive with working switches and panel lamps.
> This will be an add-on to the PiDP-11/70, giving the user even more the look
> and feel of operating a PDP-11 system 😊  The RK05 drive is constructed at the
> same scale dimensions as Oscar's PiDP-11/70 and has a front door with lock
> mechanism just like the real RK05. A real RK05 disk cartridge is 3D scanned
> and will be (scaled) 3D printed. Inside that disk cartridge is a USB stick on
> which 7 virtual RK05 "disk" container files can be stored. Jumper setting in
> the cartridge selects which container file is actually "mounted" when the
> cartrdige is mounted in the drive.

Neat.

> So far for the introduction 😊
> To make this setup work I have made changes to scp.c, scp.h, pdp11_cpu.c,
> pdp11_rk.c and the makefile, and added a few files (drive "behavior" and USB
> stick handling).
> All indicator lamps seem to behave as on the real RK05 drive ... however,
> when I do .FORMAT RK0:  (I am using RT-11)  this command always ends with
> turning on the FAULT indicator. I have added print statements to the original
> SIMH distribution in pdp11_rk.c to show the problem (so no "rubbish of mine
> interference").
> This is what I see:
>  
> PDP-11 simulator V4.0-0 Current        git commit id: 0de9b628
> sim> set rl rl02
> sim> att rl0 rt-work.dsk
> RL0: 'rt-work.dsk' Contains RT11 partitions
> 1 valid partition, Type: V05, Sectors On Disk: 10210
> sim> att rk0 rk.dsk
> RK: creating new file
> sim> boot rl0
>  
> RT-11FB  V5.03
>  
> .dir rk0:
>  
> ?DIR-F-Invalid directory
>  
> .format rk0:
> RK0:/FORMAT-Are you sure? Y
>  
>             pdp11_rk.c :: in rk_go() cyl >= RK_NUMCY
>             pdp11_rk.c :: rk_set_done() called with error 64
>  
> ?FORMAT-I-Formatting complete
>  
> .init rk0:
> RK0:/Initialzie; Are you sure? Y
>  
> .dir rk0:
>  
>  
> 0 Files, 0 Blocks
> 4762 Free blocks
>  
> .
>  
> As you can see from the printed debug statements, in the function rk_go()
> the cylinder number goes higher than the maximum number of cylinders
> possible on an RK05. Then, the function rk_set_done() is called with the
> variable "error" holding RKER_NXC (64 decimal == 000100, octal == RKER_NXC)
> ==> turns on the FAULT indicator.
> SIMH does not generate an error, all is OK, as is on the real PDP-11 / RK05.
> For now, I "solved" this by adding "if (error != RKER_NXC)", but that
> will exclude all "non-existing cylinder" errors, not only the error that
> is generated at the end of the FORMAT RK0:  command.
>  
> Is this incorrect behavior in SIMH, simulating the RK05?  I don't believe
> that, so is the RKER_NXC handled in the RK.SYS driver or in RT11 in case of
> the execution of the FORMAT command?

I only have some V2 sources.  The zero directory operation, which I think is what "format" uses, just grabs the device size and writes an empty directory.  So I'm puzzled by the reference to an invalid sector.

The driver calls that a hard error (no retrying).

But why would you turn on the FAULT light on your RK05 for that?  Fault, on the RK05, means servo failure, in particular it means the servo grid light bulb has burned out.  References to invalid disk addresses don't light FAULT in an RK05.  The Peripherals handbook describes it as (a) that light bulb failed, or (b) write current is present without a write command, meaning your disk probably has been wiped by an electronic failure.

	paul