26 Apr
2016
26 Apr
'16
2:46 p.m.
I just got some very interesting results.
I examined the bank 8 configuration register contents using the console.
It
contained 0x0136, which suggests the cache is not
valid. The base address
register contained 0x4000.
So I booted VMS and modified my code to read the same locations.
Pleasingly the code read back the same values. Which I hope means my code
is correct.
I then went back to the console to check the bank 0 configuration register
which gave me 0x0069, which indicates it is valid. So there is a good
chance I
am reading the right things.
This I think explains why I get the machine check. While in the console I
changed the bank 8 config register to 0x0137, and then I was able to read
and
write to the address of the flashbus index register,
but it didn't change
the
LEDs when I wrote to the data register, and reading
back the data register
gave me a value I didn't write. So there is still something not right,
perhaps
the other values in the bank 8 config register,
because I don't know what
they mean. However the base address seems correct as it's value is 0x4000
(the raw value in the register), and this equates to
0x1.000.0000 based on it being bits 19 upwards in the physical address
space.
I wonder if the SROM failing to read the DROM means that it does not set
up
bank 8?
It turns out that I only needed to flip the bit in the bank 8 config
register and I can now access the flashbus. I can write to the LEDs, it
turns out that writing a 0 turns the LED on, rather than off, which is why I
thought it hadn't worked.
I can now do test code for the NVRAM, I will start with repeated reads to
see if I get different values on different occasions. Then I will save it
and write patterns etc. It may be a checksum that is failing of course. Or
the DROM itself, which I can't verify until I get the PLCC adapter for my
PROM programmer and someone else to read their DROM.
Thanks for all the help I have a way forward for a little while now.
Although anyone with one of these machines who could read the DROM would be
helpful. I will be able to supply a VMS program to read it, so need to
remove it from the machine or to have a programmer.
Regards
Rob