[N8VEM: 16166] RE: ram size on cp/m

[Andrew Lynch]

Hi Antony! Thanks! Sorry to hear you are having problems with the SBC V2.
I think there is a RAM size utility or it tells you on the boot up screen.
Probably with the ROMWBW BIOS images.



Probably your best bet is to ask on the N8VEM mailing list where there are a
lot of experienced builders to help debug the SBC initial build. I have a
working SBC but it is getting quite ancient (prototype board without solder
mask, pre V1). I spend most of my hobby time designing boards and
distributing the PCBs so I don't really get into the deep debugging as much
as I would like these days.



Basically there is a methodology we sometimes use to start a reluctant
board. Every builder so far has gotten them working AFAIK. Actually if you
already have one image working to be able to boot and play Zork you are
almost certainly 99%+ there. What's left is just to verify the SRAM is
cooperating.



http://n8vem-sbc.pbworks.com/w/page/4200913/Ideas-on-how-to-fix-a-broken-boa
rd



I hope this helps!

Andrew Lynch







From: Ants Pants [mailto:rotaryboy-***@public.gmane.org]
Sent: Tuesday, September 10, 2013 8:58 PM
To: Andrew Lynch
Subject: ram size on cp/m



Hi Andrew,



question: i am having some issues with an N8VEM SBC.. most by my playing im
assuming and a case of some bad IC hardware.. but im just wandering if you
know a command in CP/M in one of the prebuilt images to tell me the size of
the current RAM installed, or a RAM checker to test that the current RAM
installed is available and working? sorry this might sound like a trivial
issue for you.. CP/M is not my strong point at the moment. i was
experiencing: getting any serial output on power-up of around 20%, after
changing a couple things i manage to get output and a hang like one user has
experienced at "loading CP/M", after changing a a few more things including
the cpu and clockrate, i get the Feb28_2009_Zork build to boot, but im
thinking i still have a RAM issue.. any help would be appreciated.



Kind Regards,

Antony

[oscarv]

Hi,

I really don't qualify as an Experienced Builder, but for just that reason
I had my share of challenges, maybe this is of some use:

Attached are some test programs - survey.com does a quick memory test, and
ramtest.com is a tougher test. You can drop them in the RomWBW's diskimg or
romdsk directory so they get included in the rom when you build it. In the
standard ROM, there is DDT so you could write a small test program in that,
if you do not feel like building a custom ROM.

Yes, RomWBW prints the RAM size on bootup, but it just prints the RAM size
that the rom image is configured for without checking the real thing
(AFAIK), so that is not much help (except that it should match the size of
your actual RAM...)

An easier way to check if the problem is ram-related is to put in another
SRAM, obviously. From what you describe, I wouldn't be sure it is
necessarily a bad RAM. I had very similar problems (only now and then the
boot string would show up on the terminal, and there were irregular freezes
afterwards if it did make it that far). My case turned out to be due to a
cheapo USB-RS232 adapter. It had trouble with the MAX232's signals. That
may be one out of a hundred possibilities, but maybe worth a quick test if
you're using a USB converter and it's not FTDI.

Maybe it's also useful to check whether the board really freezes or whether
it's just that it lost its (RS232) voice. Check if there's still pulses on
IOREQ etc when it seems to freeze?

Kind regards,

Oscar.

[Douglas Goodall]

I am not sure when you discuss ram size whether you are talking about the part visible in the lowest 64K or the other area which is used for banked OS operations and RAMDISK.

To the best of my knowledge, the RomWBW requires at least the basic 64K to be present (the old non-banked version anyway).

If it isn't already, if might be a good feature for the system to dynamically configure the RAMDISK based on the amount detected, setting up the disk parameters at book time.

Douglas

Hi,
Attached are some test programs - survey.com does a quick memory test, and ramtest.com is a tougher test. You can drop them in the RomWBW's diskimg or romdsk directory so they get included in the rom when you build it. In the standard ROM, there is DDT so you could write a small test program in that, if you do not feel like building a custom ROM.
Yes, RomWBW prints the RAM size on bootup, but it just prints the RAM size that the rom image is configured for without checking the real thing (AFAIK), so that is not much help (except that it should match the size of your actual RAM...)
An easier way to check if the problem is ram-related is to put in another SRAM, obviously. From what you describe, I wouldn't be sure it is necessarily a bad RAM. I had very similar problems (only now and then the boot string would show up on the terminal, and there were irregular freezes afterwards if it did make it that far). My case turned out to be due to a cheapo USB-RS232 adapter. It had trouble with the MAX232's signals. That may be one out of a hundred possibilities, but maybe worth a quick test if you're using a USB converter and it's not FTDI.
Maybe it's also useful to check whether the board really freezes or whether it's just that it lost its (RS232) voice. Check if there's still pulses on IOREQ etc when it seems to freeze?
Kind regards,
Oscar.
--
You received this message because you are subscribed to the Google Groups "N8VEM" group.
Visit this group at http://groups.google.com/group/n8vem.
For more options, visit https://groups.google.com/groups/opt_out.
<Survey and Ramtest.zip>

---
Douglas Goodall
doug-***@public.gmane.org
http://goodall.us.com
WQRLl515

[Wayne Warthen]

Hi Antony,

I don't have a lot to add to what has already been said, but can clarify a
couple things.

First, the RAM/ROM sizes that are listed in the startup of RomWBW are
indeed just the compile time settings. There is no concept of dynamic RAM
size determination in RomWBW. It is something that is only the enhancement
list, but pretty far down in priority.

The applications Oscar provided are probably as good as you will find right
now for testing RAM. However, the problem is that they are unaware of the
N8VEM RAM banking. The tools will only test the standard program area and
ignore the other banks. Unfortunately, there is no N8VEM specific RAM
diagnostic. This would be an excellent project for someone!!! :-) In
fact, I have often wished for a basic, generic hardware diagnostic suite
for N8VEM.

Note that RomWBW does rely heavily on memory banking. The point is that
reliable operation with RomWBW requires not only that the RAM chip itself
be good, but also that all of the associated bank switching support
circuitry works well. Some SBC V1 boards are problematic due to a design
issue with the bank switching circuit. However, SBC V2 has been
universally solid, so you should be able to get a reliable board with a
little more effort.

Based on your description of the symptoms, I think a problem with the
actual RAM chip is unlikely. I would focus on:

1. Making sure you have a solid, clean power source
2. Carefully check all solder joints with a magnifying glass
3. Carefully check chips to insure all pins are properly inserted in the
sockets and that all chips are properly oriented
4. Post a high-resolution picture here of both the top and bottom of the
PCB


Thanks,

Wayne

[Douglas Goodall]

Anthony,

In addition to Wayne's suggestions, I would like to point out a problem I have had
so you can eliminate that as well.

Sometimes when tracing signals, for instance seeing if /RD is getting to a peripheral
chip, probing the chip's pin on the top of the board may indicate a lack of activity.

When you see something like that, check the same location on the bottom of the
board as well. I have had good looking solder joints on sockets that in fact didn't
provide an adequate connection to he chip inserted. Rewarming the solder joint
and verifying continuity from the bottom of the board through the socket and up to
the actual IC pin can resolve a problem, and has for me several times.

Regards,

Douglas

Post by Wayne Warthen
Hi Antony,
I don't have a lot to add to what has already been said, but can clarify a couple things.
First, the RAM/ROM sizes that are listed in the startup of RomWBW are indeed just the compile time settings. There is no concept of dynamic RAM size determination in RomWBW. It is something that is only the enhancement list, but pretty far down in priority.
The applications Oscar provided are probably as good as you will find right now for testing RAM. However, the problem is that they are unaware of the N8VEM RAM banking. The tools will only test the standard program area and ignore the other banks. Unfortunately, there is no N8VEM specific RAM diagnostic. This would be an excellent project for someone!!! :-) In fact, I have often wished for a basic, generic hardware diagnostic suite for N8VEM.
Note that RomWBW does rely heavily on memory banking. The point is that reliable operation with RomWBW requires not only that the RAM chip itself be good, but also that all of the associated bank switching support circuitry works well. Some SBC V1 boards are problematic due to a design issue with the bank switching circuit. However, SBC V2 has been universally solid, so you should be able to get a reliable board with a little more effort.
Making sure you have a solid, clean power source
Carefully check all solder joints with a magnifying glass
Carefully check chips to insure all pins are properly inserted in the sockets and that all chips are properly oriented
Post a high-resolution picture here of both the top and bottom of the PCB
Thanks,
Wayne
--
You received this message because you are subscribed to the Google Groups "N8VEM" group.
Visit this group at http://groups.google.com/group/n8vem.
For more options, visit https://groups.google.com/groups/opt_out.

---
Douglas Goodall
doug-***@public.gmane.org
http://goodall.us.com
WQRLl515