Re: VAX RPB (Restart Parameter Block)

[Holm Tiffe <holm%freibergnet.de@localhost>]

Mouse wrote:

> >> [128 lines of quotes, not trimmed at all]
> 
> Would it be too much to ask that you trim quotes down for relevance?
> If it hadn't been in this thread I probably would have junked this
> message upon getting about 50 lines in without seeing any new text.
> 
> >    cons_A_TX: blbc    1001(r11),0x20044f32
> 
> > What does this blbc instruction?
> 
> Branch on Low Bit Clear.  Reads a longword (which for the VAX means 32
> bits, what most other 32-bit machines call a word - VAX doc tries to
> keep PDP-11 terminology, which means "word" is 16 bits) from 1001(r11).

That 1001(r11) is my question to be exact.

Needs r11 set to 0xffea00 or 0xffea01 to access the lowest bit in 0xffea01?
(0xffea01 is the DUART and DISPLAY Status, Display is bit 0x10, SLU is bit
0x1)

> If the low (least significant) bit of that longword is set, falls
> through to the next instruction; if clear, branches to 0x20044f32.

I read in the instruction description that even that only a bit is involved
in the test a longword is used for the bit adressing.

> 
> Conceptually speaking, that is.  I suspect it may actually read only
> the low byte, at least when the operand resides in normal memory; that
> the operand is defined as a longword is significant for some addressing
> modes (though not the one used in the particular case above).
> 
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T hink, the 1001 is a signed 32bit value that just adresses the 0x1 bit
in the longword (r11) points to, is that correct? ..or is in that 1001 an
additional offset regarding the pointer in r11?
(in sum I wonder about alignment und such things..)

Regards,

Holm

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