Questions/comments about rambank<n>_size parameters for Power Macintosh xx00 models

[fdanapfel]

Running dingusppc list properties shows the following properties for the Power Macintosh 8500:

Power Macintosh 8500 supported properties:

       pci_A1		insert a PCI device into A1 slot
			Valid values: Any

       pci_B1		insert a PCI device into B1 slot
			Valid values: Any

       pci_C1		insert a PCI device into C1 slot
			Valid values: Any

  adb_devices		specifies which ADB device(s) to attach
			Valid values: Any

serial_backend		specifies the backend for the serial port
			Valid values: 'null', 'stdio', 'socket'

      cdr_img		specifies path(s) to CD-ROM image(s)
			Valid values: Any

      hdd_img		specifies path(s) to hard disk image(s)
			Valid values: Any

     cdr_img2		specifies path(s) to secondary CD-ROM image(s)
			Valid values: Any

     hdd_img2		specifies path(s) to secondary hard disk image(s)
			Valid values: Any

      fdd_fmt		specifies floppy disk format
			Valid values: '', 'GCR_400K', 'GCR_800K', 'MFM_720K', 'MFM_1440K'

      fdd_img		specifies path to floppy disk image
			Valid values: Any

  fdd_wr_prot		toggles floppy disk's write protection
			Valid values: on, off, ON, OFF

 gfxmem_banks		
			Valid values: 0, 1, 2, 3

  gfxmem_size		specifies video memory size in MB
			Valid values: 0, 2, 4

       mon_id		specifies which monitor to emulate
			Valid values: Any

        vci_D		insert a VCI device 0x0D
			Valid values: Any

        vci_E		insert a VCI device 0x0E
			Valid values: Any

has_composite		
			Valid values: on, off, ON, OFF

   has_svideo		
			Valid values: on, off, ON, OFF

          cpu		specifies CPU
			Valid values: '601', '604', '604e', '750'

         emmo		enables/disables factory HW tests during startup
			Valid values: on, off, ON, OFF

rambank0_size		specifies onboard RAM bank size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank10_size		specifies RAM bank 10 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank11_size		specifies RAM bank 11 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank12_size		specifies RAM bank 12 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank1_size		specifies RAM bank 1 size in MB
			Valid values: 4, 8, 16, 32, 64, 128

rambank2_size		specifies RAM bank 2 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank3_size		specifies RAM bank 3 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank4_size		specifies RAM bank 4 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank5_size		specifies RAM bank 5 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank6_size		specifies RAM bank 6 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank7_size		specifies RAM bank 7 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank8_size		specifies RAM bank 8 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

rambank9_size		specifies RAM bank 9 size in MB
			Valid values: 0, 4, 8, 16, 32, 64, 128

Are the rambank<n>_size parmeters supposed to match the RAM slots in the real hardware?

If that is supposed to be the case, then the listedrambank<n>_size parameters don't match.

As you can see at https://support.apple.com/en-gb/112060 the Power Macintosh 8500 only has 8 RAM slots and no onboard memory.

Therefore I think there should only be rambank<1>_size to rambank<8>_size parameters for this model (only the 9x00 models had 12 RAM slots: https://support.apple.com/en-gb/112048)

Looks like the rambank_size parameters are derived from the definitions for the PowerMacintosh 7500 in

dingusppc/machines/machinetnt.cpp

Line 161 in 14b17a6

static const PropMap pm7500_settings_ ## cpu = { \

(which are also wrong; as you can see at https://support.apple.com/en-us/112073 the PM7500 also has no onboard memory and only 8 RAM slots)

By looking at the code I also found out that there is apparently a default value defined for rambank1_size:

dingusppc/machines/machinetnt.cpp

Line 163 in 14b17a6

{"rambank1_size" , new IntProperty(16, std::vector<uint32_t>({ 4, 8, 16, 32, 64, 128}))}, \

Maybe this could be mentioned in the properties, otherwise people might get confused if they set values for other rambank<n>_size parameters and then alway end up with an extra 16MB (on the real hardware it is not necessary to always have a DIMM in RAM slot 1 btw.).

Also, is interleaving supported like on real hardware. I. e. if I specify a value for rambank1_size and rambank5_size, will the OS see it as interleaved memory?

[joevt]

All the TNT and ANS machines use the same Hammerhead memory controller supporting 26 banks up to 64 MB each = 1664 MiB of RAM. The only difference is the number of physical DIMM slots that exist (2 banks per DIMM slot). There's no reason why you couldn't add more DIMM slots (except the wiring would be weird).

rambank0_size is used for bank 0 and 1 which are reserved for built-in RAM and is usually unpopulated on real Power Macs.
rambank1_size is used for bank 2 and 3.
...
rambank12_size is used for bank 24 and 25.

Perhaps the name of the property should have been ramdimm#_size but we wanted to use the same name for all machines.

7500,8500,8600 with 8 slots uses banks 2 to 17 defined by rambank1_size to rambank8_size
9500,9600 with 12 slots uses banks 2 to 25 defined by rambank1_size to rambank12_size

rambank#_size fills only the even bank number unless the size is 128 MiB. In that case, both banks get 64 MiB. I suppose there might exist 32 MiB DIMMs that fill two banks with 16 MiB each, etc.? But that doesn't matter.

If the DIMM slots contain matching pairs of DIMMs, then the HWInit code will enable the interleave bits of the Hammerhead controller but that doesn't change performance of emulated hardware. The HWInit code is the same in all the TNT machines. It will scan all 26 banks.

Apple Network Server ROM has a HWInit that only works with 512 MiB max. We allow more RAM for that so you can see how it fails in case you want to create a better ROM.

We have a default for one of the RAM slots so that you don't have to specify RAM sizes to boot something. Of course, that doesn't work for OS's that require more than 16 MiB but at least you can boot into Open Firmware. I suppose what's missing is the ability to set the first DIMM to 0 MiB. Booting with no RAM is a valid test of the emulation and should be allowed.

Here's code to dump Hammerhead registers in Open Firmware:

\ Dump Hammerhead memory registers

\ MSB LSB
\ 0:4 Reserved					F8
\ 5 Interleave Enable			04
\ 6 Address Mode				02
\ 7 Base Addr [1]				01
\ 8:15 Base Addr [2..9]

: dump-hammerhead-dimms
	F8000500 f80001C0 do
		cr i 8 u.r ." : dimm:"
		i f80001C0 - 40 / dup a < if space then .d ." bank:"
		i f80001C0 - 20 / dup a < if space then .d ." flags:"
		i c@ dup fe and 2 u.r ."  address:"
		1 and d# 30 << i 10 + c@ d# 22 << or 8 u.r
	20 +loop
	cr
	;
	
dump-hammerhead-dimms

This is what 1 GiB in my real Power Mac 8600 looks like:

F80001C0: dimm: 0 bank: 0 flags:00 address:00000000
F80001E0: dimm: 0 bank: 1 flags:00 address:00000000
F8000200: dimm: 1 bank: 2 flags:04 address:00000000
F8000220: dimm: 1 bank: 3 flags:00 address:08000000
F8000240: dimm: 2 bank: 4 flags:04 address:08000000
F8000260: dimm: 2 bank: 5 flags:00 address:10000000
F8000280: dimm: 3 bank: 6 flags:04 address:10000000
F80002A0: dimm: 3 bank: 7 flags:00 address:18000000
F80002C0: dimm: 4 bank: 8 flags:04 address:18000000
F80002E0: dimm: 4 bank: 9 flags:00 address:20000000
F8000300: dimm: 5 bank:10 flags:04 address:20000000
F8000320: dimm: 5 bank:11 flags:00 address:28000000
F8000340: dimm: 6 bank:12 flags:04 address:28000000
F8000360: dimm: 6 bank:13 flags:00 address:30000000
F8000380: dimm: 7 bank:14 flags:04 address:30000000
F80003A0: dimm: 7 bank:15 flags:00 address:38000000
F80003C0: dimm: 8 bank:16 flags:04 address:38000000
F80003E0: dimm: 8 bank:17 flags:00 address:40000000
F8000400: dimm: 9 bank:18 flags:00 address:40000000
F8000420: dimm: 9 bank:19 flags:00 address:40000000
F8000440: dimm:10 bank:20 flags:00 address:40000000
F8000460: dimm:10 bank:21 flags:00 address:40000000
F8000480: dimm:11 bank:22 flags:00 address:40000000
F80004A0: dimm:11 bank:23 flags:00 address:40000000
F80004C0: dimm:12 bank:24 flags:00 address:40000000
F80004E0: dimm:12 bank:25 flags:00 address:40000000

Read the Hammerhead_ERS_Rev_1.1_19950925.pdf document to understand what these values mean.
You see that all the DIMM pairs are interleaved (the interleave flag is specified in the even bank registers).

[joevt]

Made this commit to my fork:
machinetnt: Allow 0 MiB of RAM.

This DBDMA program plays the system startup chime:

    ffe00020(ro): 00.00.8000 ffe000a0 00000000 0000.0000 : OUTPUT_MORE  STREAM0     req:32768  adr:ffe000a0
    ffe00030(ro): 00.00.8000 ffe080a0 00000000 0000.0000 : OUTPUT_MORE  STREAM0     req:32768  adr:ffe080a0
    ffe00040(ro): 00.00.8000 ffe100a0 00000000 0000.0000 : OUTPUT_MORE  STREAM0     req:32768  adr:ffe100a0
    ffe00050(ro): 00.00.8000 ffe180a0 00000000 0000.0000 : OUTPUT_MORE  STREAM0     req:32768  adr:ffe180a0
    ffe00060(ro): 00.00.8000 ffe200a0 00000000 0000.0000 : OUTPUT_MORE  STREAM0     req:32768  adr:ffe200a0
    ffe00070(ro): 00.00.8000 ffe280a0 00000000 0000.0000 : OUTPUT_MORE  STREAM0     req:32768  adr:ffe280a0
    ffe00080(ro): 10.00.2b60 ffe300a0 00000000 0000.0000 : OUTPUT_LAST  STREAM0     req:11104  adr:ffe300a0
    ffe00090(ro): 70.00.0000 00000000 00000000 0000.0000 : STOP

It does the first two DBDMA commands while checking the RAM. The RAM test fails (no RAM installed) so it aborts that program and starts this DBDMA program to play the crash sound:

    ffe40020(ro): 10.00.6238 ffe40040 00000000 0000.0000 : OUTPUT_LAST  STREAM0     req:25144  adr:ffe40040
    ffe40030(ro): 70.00.0000 00000000 00000000 0000.0000 : STOP