L4 on MIPS R4x00: Answers to Frequently Asked Questions

Is there a chance to run it on an R3000?
Not easily. You'd have to deal with some of the problems mentioned for the R5000 below. The main problem, however, is that L4/MIPS is a fair dinkum 64-bit kernel while the R3000 is a 32-bit machine.
[99-08-29]
How much effort would be involved to port to platform X (where X != MIPS).
I'd say a complete re-write would be involved. Very little code is not MIPS dependent.
[98-01-27]
What's involved in getting it going on an R5000?
The following issues are involved.
- Code is dependent on the 16K data cache size, I don't know what is on the R5000,
- Code is specific to the R4x00 TLB,
- Co-processor hazards are for R4700,
- Some code is tuned to the R4700 pipeline,
- Code only tested on R4600/R4700,
- Serial I/O may need redoing for new box.
We currently have no plans (and no hardware) to tackle the above.
[98-01-27]
I get a page fault from a "user" task with a funny IP value like 0xffffffff8005b244, while the fault address is a more reasonable address within the executable image. The IP value seems to be an invalid address, and I anyway have never mapped such a page to the client. How can the code be executing there?
It means that the page fault happens during a system call, when L4 tries to access user data (e.g. during a long IPC operation). You probably have a string dope pointing to the wrong place.
[97-09-10]
I keep getting messages like:
SIGMA0 INFO: mapping request to sigma0 out of available memory range thread id 0x1002000000081801, address 0x1c, IP 0x6cc90
What does this mean, and what can I do about it?
It means that you are trying to access kernel-reserved memory. The most likely reasons for this are:
- dereferencing an uninitialised pointer, or
- overwriting the stack
Remember, you are the operating system, hence there is nobody to protect you from your own mistakes.
To eliminate these error messages, make certain that all pointers are properly initialised. Use assert(p) if in doubt.
Also make sure you are not overflowing your stack. It is safest not to put arrays or large records on the stack, declare them as static. Note that you can use the static storage class also for a function's local variables, that way you do not lose the locality local variables give you. However, be aware that you may have to use concurrency control on local static variables if the function can be called from different threads.
[97-09-09]

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