|
|---|
Marcel Verdaasdonk
Netherlands
| |
Posts 3991
01 Jun 2012 15:00
| This is the memory located at C00000.()
Sources vary on how much is there between 512Kb and 1.5Mb.(some even 2Mb with tricks)
IMHO this is a cludge however I have found that some programs refuse to work without fastmem check for this space.
Which is ironic since this is no fastmem, it is blocked by the chipset since it generates the RAS & CAS for this space.What to do with this?
I am sure we talked about this before.
| |
Sascha B
Germany
| |
Posts 131
01 Jun 2012 15:34
| Standard trapdoor epansion has 512KB of slowram.
Others with additional Gary Adapter can handle up to 1.8MB.
Many old game depend on "some slowram" at $c00000, I think at least 256-512KB should work.
Without that the game dont work at all due to direct address usage without allocating via kickstart routine.
In Minimig this memory can be set via OSD of 0-1.5MB in 0.5MB steps.
| |
SID Hervé
France
| |
Posts 666
01 Jun 2012 20:31
| This additional memory (for A500 and A2000) can act as chip-ram or as fast ram. It is a cheap extension. Access may be temporarily prohibited to specialized circuits which can slow down the CPU access. That said, thanks for the additional details ("it generates the RAS & CAS for this space." and "Other with additional Gary Adapter can handle up to 1.8MB.")
| |
Marcel Verdaasdonk
Netherlands
| |
Posts 3991
01 Jun 2012 22:35
| to be honest there is one more minor detail about this but that shouldn't affect this project and that is in a A500 typically the main memory uses Fast Page Memory with a access time of either 80ns or 70ns.
For the C00000 addressed space a access time of 120ns is normal.
Again this is rather pointless information.BTW up to DC0000 can be used since the RTC starts on that address.
this is about 1.75Mb, of course Gayle spoils our fun. ;)
Dave Haynie's PLD source code even limits it to 1Mb with CPU expansion card on A2000's which NEVER used this region for expansion memory!!!(AFAIK)
| |
Sascha B
Germany
| |
Posts 131
02 Jun 2012 16:05
| OCS and ECS is able to work with up to 150ns of chipmem/slowmem access time.
Any faster memory is just luxury and do not affect system speed.
| |
Thierry Atheist
Canada
| |
Posts 1830
06 Jun 2012 12:09
| "A500 Magic Memory"? Hi Marcel, do you really mean "A1200 Magic Memory"??? EXTERNAL LINK
EXTERNAL LINK
Seriously, I've never owned one, will get two of..... and more NatAmis than that when they arrive!!!!!!
| |
Sascha B
Germany
| |
Posts 131
06 Jun 2012 14:06
| BTW in very first Amiga2000 Rev.4 (Braunschweig 4 layer pcb) with DIP-Agnus as in A1000, this $C00000 expansion card for the "MMU slot" actually is Fast-RAM.
Only newer Amiga 500/2000 model with FatAgnus chip called this "Slow RAM". Reason is that FatAgnus is able to address this range (as pseudo chipmem) and generate all necessary bus signal for the CPU. Also Agnus blocks CPU while DMA memory access to Chipmem.
In general the (CPU) access speed to this area is not important.
More important is the existing of at least 512kb RAM at the mentioned address to let some older game/demo title work.
Those title don't use Kickstart memory allocation but just direct access this area to store data.
If missing the title may crash or stall.
| |
Thomas Richter
Germany
| | (MX-Board Owner)
Posts 1425
06 Jun 2012 15:06
| Sascha B wrote:
|
BTW in very first Amiga2000 Rev.4 (Braunschweig 4 layer pcb) with DIP-Agnus as in A1000, this $C00000 expansion card for the "MMU slot" actually is Fast-RAM.
|
Was this really rev.4? I believe my A2000B (two-layer model) was a rev 4.1. Of course, there this memory is "slow". Well-made combination of the drawbacks of both memory types.
| |
Sascha B
Germany
| |
Posts 131
07 Jun 2012 09:04
| Thomas Richter wrote:
|
Was this really rev.4? I believe my A2000B (two-layer model) was a rev 4.1. Of course, there this memory is "slow". Well-made combination of the drawbacks of both memory types.
|
Yes it is labled as "Rev. 4" without .x
I own 2 of this boards, here are some picture: EXTERNAL LINK
In this system the $C00000 memory is faster than in A500 and newer A2000 model, trust me.
| |
|
Do you have ideas and feature wishes? Post them here and discuss your ideas.