Saturday, September 24, 2011

CD-i 180 internals

In the previous post I promised some ROM and chip finds. Well, here goes. To understand some of the details, you'll need some microprocessor and/or digital electronics knowledge, but even without that the gist of the text should be understandable.

The CDI 181 MMC unit contains the so-called Maxi-MMC board that is not used in any other CD-i player. Its closest cousin is the Mini-MMC board that is used in the CD-i 605 and CD-i 220 F1 players (a derivative of it is used in the CD-i 350/360 players).

The Mini-MMC board uses two 68HC05 slave processors for CD and pointing device control (they are usually called SERVO and SLAVE). The Maxi-MMC board does not have these chips, but it does have two PCF80C21 slave processors labeled RSX and TRANSDUCER that perform similar functions.

From their locations on the board I surmise that the RSX performs CD control functions; I know for sure that the TRANSDUCER performs only pointing device control. The latter is connected to the main 68070 processor via an I2C bus (I've actually traced the connections); I'm not completely sure yet about the RSX.

In order to emulate the pointing devices in CD-i Emulator, I had to reverse engineer the I2C protocol spoken by the TRANSDUCER chip; this was mostly a question of disassembling the "ceniic" and "periic" drivers in the ROM. The first of these is the low-level driver that serves as the common control point for the I2C bus; the second is the high-level driver that is instantiated separately for each type of pointing device. The ROMs support three such devices: /cdikeys, /ptr and /ptr2, corresponding to the player control keys and first and second pointing devices (the first pointing device is probably shared between the infrared remote sensor and the left pointing device port). Both pointing devices support absolute (e.g. touchpad) as well as relative (e.g. mouse) positioning.

Note that there is no built-in support for a CD-i keyboard or modem (you could use a serial port for this purpose).

However, knowing the I2C protocol does not tell me the exact protocol of the pointing devices, which therefore brings me no closer to constructing a "pointing device" that works with the two front panel MiniDIN-9 connectors. Note that these connectors are physically different from the MiniDIN 8 pointing device connectors used on most other CD-i players. According to the Philips flyers, these connectors have 6 (presumably digital) input signals and a "strobe" (STB) output signal. From the signal names I can make some educated guesses about the probable functions of the signals, but some quick tests with the BTN1 and BTN2 inputs did not pan out and it could be too complicated to figure out without measurement of a connected and working pointing device.

There is, however, also an infrared remote sensor that is supposed to expect the RC5 infrared signal protocol. This protocol supports only 2048 separate functions (32 groups of 64 each) so it should not be impossible to figure out, given a suitably programmable RC5 remote control or in the best case a PC RC5 adapter. I've been thinking about building one of the latter.

There is also a third possibility of getting a working pointing device. Although the case label of the front MiniDIN 8 connecter is "CONTROL", the Philips flyers label it "IIC" which is another way of writing "I2C", although they don't give a pinout of the port. It seems plausible that the connector is connected to the I2C bus of the 68070, although I haven't been able to verify that yet (the multimeter finds no direct connections except GND, so some buffering must be involved). If there is indeed a connection, I would be able to externally connect to that bus and send and receive the I2C bus commands that I've already reverse engineered.

If even this doesn't work, I can always connect directly to the internal I2C bus, but that involves running three wires from inside the player to outside and I'm not very keen on that (yet, anyway).

Now, about the (so far) missing serial port. There is a driver for the 68070 on-chip UART in the ROMs (the u68070 driver which is accessible via the /t2 device), and the boot code actually writes a boot message to it (CD-i Emulator output):
  PHILIPS CD-I 181 - ROM version 23rd January, 1992.
Using CD_RTOS kernel edition $53 revison $00
At first I thought that the UART would be connected to the "CONTROL" port on the front, but that does not appear to be the case. Tonight I verified (by tracing PCB connections with my multimeter) that the 68070 serial pins are connected to the PCB connector on the right side (they go through a pair of SN75188/SN75189 chips and some protection resistors; these chips are well-known RS232 line drivers/receivers). I even know the actual PCB pins, so if I can find a suitable 100-pins 0.01" spaced double edge print connector I can actually wire up the serial port.

Now for the bad news, however: the ROMs do not contain a serial port download routine. They contain a host of other goodies (more below) but not this particular beast. There is also no pointing device support for this port, contrary to all other players, so connecting up the serial port would not immediately gain me anything, I still need a working pointing device to actually start a CD-i disc…

There are no drivers for other serial ports in the ROMs, but the boot code does contain some support for a UART chip at address $340001 (probably a 68681 DUART included in the CDI 182 unit which I don't have). The support, however, is limited to the output of boot messages although the ROMs will actually prefer this port over the 68070 on-chip device if they find it.

As is to be expected from a development and test player, there is an elaborate set of boot options, but they can only be used if the ROMs contain the signature "IMS-TC" at byte offset $400 (the ROMs in my player contains FF bytes at these locations). And even then the options prompt will not appear unless you press the space bar on your serial terminal during player reset.

However, adding a -bootprompt option that handles both the signature and the space bar press to CD-i Emulator was not hard, and if you use that option with the 180 ROMs the following appears when resetting the player:
  PHILIPS CD-I 181 - ROM version 23rd January, 1992.

A-Z = change option : <BSP> = clear options : <RETURN> = Boot Now

Boot options:- BQRS
As specified, you can change the options by typing letters and pressing Enter will start the boot process with the specified options.

From disassembling the boot code of the ROMs I've so far found the following options:

D = Download/Debug
F = Boot from Floppy
L = Apply options and present another options prompt (Loop)
M = Set NTSC Monitor mode
P = Set PAL mode
S = Set NTSC/PAL mode from switch
T = Set NTSC mode
W = Boot from SCSI disk (Winchester)

It could be that there's also a C option, and I've as yet not found any implementations of the Q and R options that the ROMs include in the default, but they could be hidden in OS-9 drivers instead of the boot code.

Once set, the options are saved in NVRAM at address $313FE0 as default for prompts during subsequent reboots, they are not used for reboots where the option prompt is not invoked.

Options D, F and W look interesting, but further investigation leads to the conclusion that they are mostly useless without additional hardware.

Pressing lower-case D followed by Enter / Enter results in the following:
Boot options:- BQRSd
Boot options:- BDQRS
Enter size of download area in hex - just RETURN for none
called debugger

Rel: 00000000
Dn: 00000000 0000E430 0007000A 00000000 00000000 00000001 FFFFE000 00000000
An: 00180B84 00180570 00313FE0 00410000 00002500 00000500 00001500 000014B0
SR: 2704 (--S--7-----Z--) SSP: 000014B0 USP: 00000000
PC: 00180D2E - 08020016 btst #$0016,d2
One might think that entering a download size would perform some kind of download (hopefully via the serial port) but that is not the case. The "download" code just looks at location $2500 in RAM that's apparently supposed to be already filled (presumably via an In-Circuit Emulator or something like it).

However, invoking the debugger is interesting in itself. It looks like the Microware low-level RomBug debugger that is described in the Microware documentation, although I haven't found it in any other CD-i players. One could "download" data with the change command:
debug: c0
00000000 00 : 1
00000001 00 : 2
00000002 15 : 3
00000003 00 :
Not very userfriendly but it could be done. The immediate catch is that it doesn't work with unmodified ROMs because of the "IMS-TC" signature check!

Trying the F option results in the following:
Boot options:- BQRSf
Boot options:- BFQRS
Booting from Floppy (WD 179x controller) - Please wait
This, however, needs the hardware in the CDI 182 set (it lives at $330001). I could emulate that in CD-i Emulator of course, but there's no real point at this time. It is interesting to note that the floppy controller in the CD-i 605 (which I haven't emulated either at this point) is a DP8473 which is register compatible with the uPD765A used in the original IBM PC but requires a totally different driver (it also lives at a different memory address, namely $282001).

Finally, trying the W options gives this:
Boot options:- BQRSw
Boot options:- BQRSW
Booting from RODIME RO 650 disk drive (NCR 5380 SCSI) - Please wait
Exception Error, vector offset $0008 addr $00181908
Fatal System Error; rebooting system
The hardware is apparently supposed to live at $410000 and presumably emulatable; it's identical or at least similar to the DP5380 chip that is found on the CD-i 605 extension board where it lives at $AA0000).

Some other things that I've found out:

The CDI 181 unit has 8 KB of NVRAM but it does not use the M48T08 chip that's in all other Philips players, it's just a piece of RAM that lives at $310000 (even addresses only) and is supported by the "nvdrv" driver via the /nvr device.

In the CD-i 180 player the timekeeping functions are instead performed by a RICOH RP5C15 chip, the driver is appropriately called "rp5c15".

And there is a separate changeable battery inside the case; no "dead NVRAM" problems with this player! I don't know when the battery in my player was last changed but at the moment it's still functioning and had not lost the date/time when I first powered it on just over a week ago.

The IC CARD slot at the front of the player is handled like just another piece of NVRAM; it uses the same "nvdrv" driver but a different device: /icard. According to the device descriptor it can hold 32 KB of data, I would love to have one of those!

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