1 $NetBSD: VMEbus-RAM,v 1.1 2002/01/12 19:29:49 scw Exp $ 2 3NetBSD/mvme68k: VMEbus RAM card configuration 4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 5 6NetBSD-mvme68k can be configured to support additional RAM boards 7accessed over the VMEbus. 8 9This file describes where to configure your VMEbus RAM and how to 10point the kernel in the direction of it. 11 12The MVME147 board has a fairly primitive VMEbus controller chip. The 13mapping of cpu address to VMEbus address is hardwired and so dictates 14what can be seen where by the 68030. From the cpu's perspective, A24 15space spans 0x00000000 to 0x00ffffff. However, onboard RAM also spans 16this space. With 8Mb of onboard RAM, only the top 8Mb of VMEbus A24 17space can be seen. With 16Mb onboard, there is no easy way to get at 18A24 space at all! 19 20The other MVME boards have a more sophisticated VMEbus controller 21which can remap segments of VMEbus address space anywhere in the CPU's 22address space. This document will assume the remap is `transparent', 23ie. no translation is taking place. The same restriction as MVME147 24applies to these boards in that, without translation, a region of 25VMEbus address space is masked by onboard RAM. The size of this region 26depends entirely on the size of onboard RAM. 27 28The best place for VMEbus RAM cards is somewhere in A32D32 VMEbus address 29space. Obviously, if your VMEbus RAM card doesn't respond to that space 30then you'll have to locate it elsewhere. Typically, you may find it 31responds to A24D16 only, in which case the CPU-relative address you need 32to specify below will be in the 16MB region starting at 0xZZZZZZZZ. 33 34For A32D32, choose an address which is resonably close to the end of the 35MVME board's RAM. That is, if you have 32MB of onboard RAM, set the 36VMEbus RAM board to appear at A32:02000000. 37 38This starting address needs to be written to the MVME board's NVRAM at 39address 0xfffe0764 for MVME147, and 0xff, as follows: 40 41 147Bug> mm fffe0764 ;L 42 FFFE0764 00000000? 01000000 <cr> <--- you type 01000000 43 FFFE0768 00000000? . <cr> 44 147Bug> 45 46Next, you need to configure the end address of VMEbus RAM. Assuming 47your RAM card is 8Mb in size, this would be 0x017fffff. You need to 48write this value to NVRAM address 0xfffe0768, as follows: 49 50 147Bug> mm fffe0768 ;L 51 FFFE0768 00000000? 017fffff <cr> <--- you type 017fffff 52 FFFE076c 00000000? . <cr> 53 147Bug> 54 55You could obviously combine the above two steps. 56 57If you have more than one VMEbus RAM card, you must configure them so 58that they appear physically contiguous in A32 address space. So, to add 59another 8Mb card in addition to the card above, it should be jumpered 60to start at 0x01800000. In this case, you would change NVRAM location 610xfffe0768 to be 0x01ffffff. 62 63If NVRAM location 0xfffe0764 is zero, the kernel assumes you only have 64onboard RAM and will not attempt to use any VMEbus RAM. 65 66 67Some extra notes on VMEbus RAM cards 68~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 69 70So... You've got your nice shiny VMEbus RAM card up and running with 71NetBSD, and you're wondering why your system runs slower than it did 72with less RAM! 73 74The simple answer is "Motorola got it wrong". (Or at least that's my 75opinion. If anyone can cure the following, let me know!) 76 77In their infinite wisdom, the designers of the MVME147 decided that 78they would disable the 68030's cache on *any* access to the VMEbus. 79The upshot is that the cache only works for onboard RAM, not VMEbus 80RAM, hence your system runs slower. As far as I can see, the only 81way to cure this is to physically cut a trace on the circuit board 82and use the MMU to control caching on a page-by-page basis... 83 84Anyhow, hopefully the above instructions have finally put to rest 85the most asked question about the mvme68k port. 86 87Cheers, 88Steve Woodford: scw@netbsd.org 89