Re: Does the KA630 have a TB?

[Johnny Billquist <bqt%softjar.se@localhost>]

Yes, it has a translation buffer. I don't know offhand the size of it. 
But you can see about the TBIA and TBIS in 
https://bitsavers.org/pdf/dec/vax/630/EK-KA630-UG-001_Feb86.pdf, chapter 4.8

But I seriously doubt the translation buffer in the uVAX II covers 
anything close to 8M. But I also fail to see that it would matter 
exactly how big it is. The population of the TB is done completely 
hidden from the OS. And I have a hard time thinking that NetBSD would 
depend on any specific size of the TB.

I would rather suspect that there is something wrong in your implementation.

  Johnny

On 2023-09-24 13:28, Mouse wrote:
> Does anyone happen to know whether the KA630 (the MicroVAX-II) has a
> translation buffer, and if so how big it is and what its replacement
> policy is?
>
> I added a translation buffer to my emulator and promptly got crashes
> from the NetBSD version I'm running on it.  My translation buffer is
> big enough to hold a full 8M of mappings (I could have got away with
> 6M, but it didn't seem worth the additional code complexity).  On
> digging, it seems that the NetBSD version I'm trying to use is missing
> some mtpr(0,PR_TBIA) calls.
>
> This led me to wonder how it ever worked on that hardware (which it
> did; it's what I ran back when I was running my real KA630).  The only
> conclusions I can come to are (1) either the KA630 doesn't have a TB
> (which sounds very nonperformant - each userland VM access would
> involve two additional trips to main memory) or (2) it does, but its
> size combined witih its replacement policy are such that the stale
> mappings got flushed before they mattered.
>
> I could just fix the kernel to TBIA/TBIS more correctly (and as an
> interim step that's exactly what I'm doing).  But I'd like to make my
> emulation more accurate, if enough information to do so is publicly
> available.
>
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