In message <885489B3B89FB6449F93E525DF78777F064542 at srvnt506.ALLOPTIC.COM> you wrote: > > I can see if I mmap the internal 860 CPU registers, and screw up that, I > will > definitely screw up the system, and require it to be reboot. BUt if the > hardware we are mapping is outside the CPU internal memory and outside the > RAM, > shouldn't the failure be limited to the user application only then?
No. For example, assume there is a port pin which is meant as an input, and the signal is driven from external hardware. Now your application program by mistake re-programs this pin as output. You may smoke your board this way. > only the memory regions that is mapped to the ethernet switching chip, > even if I screw up on the hardware setup, shouldn't my kernel still be > protected? At most, the application faults and I should be able to restart > the application without rebooting the system? There is a simple rule: if you open backdoors in a secure system the result is an insecure system. Write clean code. There is many things you have to keep in mind: * Functionality: you cannot process interrupts in user space * Performance: how do you synchronize your accesses to the hardware? * Communication: How do you know when data has been processed, or has become available, or stable, or ...? * Tricky things: What will the caches in your system do when the application accesses the hardware? How will you address memory? Remember that there are systems where a 32 bit address is not sufficient any more... etc. etc. Write clean code. Wolfgang Denk -- Software Engineering: Embedded and Realtime Systems, Embedded Linux Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de Life is a game. Money is how we keep score. - Ted Turner ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
