AlphaStation 200 NVRAM Problem
robert.jarratt at ntlworld.com
Tue Apr 26 16:46:22 CDT 2016
> I just got some very interesting results.
> I examined the bank 8 configuration register contents using the console.
> 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
> 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
> write to the address of the flashbus index register, but it didn't change
> 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,
> 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
> I wonder if the SROM failing to read the DROM means that it does not set
> 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.
More information about the cctech