Re: I/O bus reset to fix CMD MSCP controllers (and probably others)

Actually, udamatch() confuse me. I don't understand how it is expected 
to deal with step 3 and 4. And we have a proper initialization in 
mscp/mscp_subr.c in mscp_init(), which also walks through all the 
initialization steps.

I honestly don't understand the thinking behind that code...

   Johnny

On 2025-03-29 02:18, Johnny Billquist wrote:
> Hmm. I haven't read through all the code, but I at least see some problems.
> 
> In the initialization, the code looks like this:
> 
>          bus_space_write_2(mi.mi_iot, mi.mi_iph, 0, 0); /* Start init */
>          if (mscp_waitstep(&mi, MP_STEP1, MP_STEP1) == 0)
>                  return 0; /* Nothing here... */
> 
> 
> and so on for the next step. The problem is that mscp_waitstep then only 
> checks that the controller moves to the next step, but cannot detect if 
> the controller indicates any error.
> The first MP_STEP1 really should be ALLSTEPS, and there should be some 
> code to do a reset for a second try in case you see an error condition.
> 
> But actually, even more proper should be to use STEP1MASK and compare 
> against STEP1GOOD, and so on... There are all these nice values defined 
> in mscp/mscpreg.h, but then they are not used, and we have this half- 
> broken code instead. I wonder how that happened...?
> 
>    Johnny
> 
> On 2025-03-28 18:59, Hans Rosenfeld wrote:
>> On Fri, Mar 28, 2025 at 05:27:48PM +0100, Johnny Billquist wrote:
>>>
>>> Here is the actual patch:
>>>
>>> *** usr/src/sys/conf/boot/raboot.s.old  Mon Aug 17 21:41:34 2009
>>> --- usr/src/sys/conf/boot/raboot.s      Mon Aug 17 22:44:12 2009
>>> ***************
>>> *** 1,5 ****
>>> --- 1,9 ----
>>>    /*
>>>     *    SCCS id @(#)raboot.s    2.0 (2.11BSD)   4/13/91
>>> +  *
>>> +  * Code corrected as per the other primitive mscp drivers
>>> +  * to handles other mscp controllers than DECs.
>>> +  * /bqt - 20090817
>>>     */
>>>    #include "localopts.h"
>>>
>>> ***************
>>> *** 59,65 ****
>>>
>>>    MSCPSIZE =    64.    / One MSCP command packet is 64bytes long 
>>> (need 2)
>>>
>>> ! RASEMAP       =       140000  / RA controller owner semaphore
>>>
>>>    RAERR =               100000  / error bit
>>>    RASTEP1 =     04000   / step1 has started
>>> --- 63,69 ----
>>>
>>>    MSCPSIZE =    64.    / One MSCP command packet is 64bytes long 
>>> (need 2)
>>>
>>> ! RASEMAP       =       100000  / RA controller owner semaphore
>>>
>>>    RAERR =               100000  / error bit
>>>    RASTEP1 =     04000   / step1 has started
>>> ***************
>>> *** 153,170 ****
>>>          mov     $RASEMAP,*$ra+RARSPH    / set mscp semaphores
>>>          mov     $RASEMAP,*$ra+RACMDH
>>>          mov     *_bootcsr,r0            / tap controllers shoulder
>>> !       mov     $ra+RACMDI,r0
>>>    1:
>>>          tst     (r0)
>>> !       beq     1b                      / Wait till command read
>>> !       clr     (r0)+                   / Tell controller we saw it, ok.
>>>    2:
>>>          tst     (r0)
>>> !       beq     2b                      / Wait till response written
>>>          clr     (r0)                    / Tell controller we got it
>>>          rts     pc
>>>
>>> ! icons:        RAERR
>>>          ra+RARING
>>>          0
>>>          RAGO
>>> --- 157,176 ----
>>>          mov     $RASEMAP,*$ra+RARSPH    / set mscp semaphores
>>>          mov     $RASEMAP,*$ra+RACMDH
>>>          mov     *_bootcsr,r0            / tap controllers shoulder
>>> !       mov     $ra+RACMDH,r0
>>>    1:
>>>          tst     (r0)
>>> !       bmi     1b                      / Wait till command read
>>> !       mov     $ra+RARSPH,r0
>>>    2:
>>>          tst     (r0)
>>> !       bmi     2b                      / Wait till response written
>>> !       mov     $ra+RACMDI,r0
>>> !       clr     (r0)+                   / Tell controller we saw it, ok.
>>>          clr     (r0)                    / Tell controller we got it
>>>          rts     pc
>>>
>>> ! icons:        RAERR + 033
>>>          ra+RARING
>>>          0
>>>          RAGO
>>>
>>>
>>>
>>> Anyway, not sure if this helps, since now we're in PDP-11 assembler. But
>>> maybe it gives a bit of an idea what the problem was.
>>
>> I've actually looked at that and tried to understand it when I was
>> looking into this issue. The PDP-11 assembly doesn't scare my, I've
>> written my fair share of it and I'm still comfortable reading it. Too
>> bad the patch doesn't show the definiton of RACMDI and RARSPH, and I'm
>> too lazy to google that. Maybe I'll boot the 11/73 later this weekend
>> and look at the full code.
>>
>> What I did read was the MSCP programming document for the UDA50 that's
>> on Bitsavers.
>>
>>> But if someone points me at the specific code in NetBSD, I can try to 
>>> see if
>>> it's a similar kind of issue.
>>
>> The problem is in sys/dev/qbus/uda.c, in particular in udamatch(). All
>> that udamatch() wants to do is to go through the first initialization
>> steps to cause an interrupt.
>>
>> The state of the controller when udamatch() is running is that it has
>> been used already by VMB and boot to get the kernel loaded.
>>
>> The UDA50 register interface really consists only of two registers, IP
>> and SA. Writing anything into IP should cause a initialization sequence
>> to be started, with SA indicating Step1 shortly after. If it doesn't,
>> udamatch() should try one more time, but currently doesn't. It only
>> retries the initialization if Step1 was reached and we then fail to
>> reach Step2.
>>
>> The first thing I did was checking that the CSR was mapped correctly,
>> that the physical addresses where what was expected. I also read and
>> wrote the registers directly at the VMB console. It would have been
>> surprising if anything was wrong there, as the same code works just fine
>> when the controller hasn't been touched since the last I/O bus reset
>> since we've booted off the network.
>>
>> One of the things I did as an experiment was have udamatch() write 0
>> into SA, and then read it once per second until something happened. Most
>> of the time, SA would have the error bit set after a few seconds. From
>> there, writing 0 into IP would kick off a controller initialization and
>> get SA to indicate Step1 2s later. But as I said, this incurs a boot
>> delay around 12s.
>>
>>
>> Hans
>>
>>
> 

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: [email protected]             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol