On Tue, 15 Mar 2011 14:21:03 -0500 Timur Tabi timur@freescale.com wrote:
On Sun, Mar 13, 2011 at 10:46 AM, Jimi Xenidis jimix@watson.ibm.com wrote:
Turns out that TSR[DIS] was on when my program took over, and this is ePAPR legal. I need to reset the DEC in my code.
I wonder if it should be legal. What value does it have to leave a pending decrementer interrupt when booting the OS? That just forces every OS to program the decrementer and clear DIS before enabling interrupts.
The OS should ensure that timer interrupts are functioning the way it wants before it enables interrupts -- but in any case, once it enables interrupts it should be able to handle any interrupt that is enabled. There's no general need to clear DIS.
There's actually no good way for boot software to ensure that TSR[DIS] is clear, other than stopping the timebase (not allowed, or at least shouldn't be), or assuming that the OS will take control of the decrementer within a reasonable amount of time. We could require that TCR[DIE] be clear, but that just imposes an extra requirement on boot software for no good reason -- and in general, we want to minimize the extent to which we trust boot software to do something specific. Especially if it's something that won't show up as a problem with most client software, until someone decides to rely on it.
-Scot