20 Feb
2008
20 Feb
'08
3:45 p.m.
On 20 Feb 2008 at 13:28, Glen Slick wrote:
From a quick scan of the comments it appears that the
IBL firmware
handler recognizes I/O instructions as it unpacks them from the loader
PROM and fixes them up on the fly if the select code is less than 10.
Greater than or equal to 10 (it leaves select codes less than 10, e.g.,
DCPC instructions, alone). It actually adds SC-10 as derived from the S
register to the I/O instructions. This is how it can configure both select
codes of a two-card device (e.g., 7900 disc) from the single select code
entered via the front panel.
On 20 Feb 2008 at 14:05, Tim Riker wrote:
It also presumably needs to update address offsets as
the code is
relocated?
IBL MRG instructions reference the current page, i.e., contain only the
offset from the current page, so they are relocatable to any page. In
practice, the microcode copies the ROM into the last page of physical
memory <= 32K.
Any pointers on why IBL won't work on my HP-2108A
? :)
Bad ROM? I presume you've tried storing values into the last 64 locations
in memory via the front panel to confirm that writing memory works. You
might try a scope on the ROM outputs to see if they move when you press the
IBL button.
-- Dave