[OpenBIOS] [PATCH] Add tbu@ and tbl@ words
balaton at eik.bme.hu
Wed Dec 27 22:27:31 CET 2017
On Wed, 27 Dec 2017, Programmingkid wrote:
>> On Dec 27, 2017, at 1:48 PM, Segher Boessenkool <segher at kernel.crashing.org> wrote:
>> On Wed, Dec 27, 2017 at 01:35:46PM -0500, John Arbuckle wrote:
>>> +/* reads the lower timebase register ( -- tbl ) */
>>> +static void get_tbl(void)
>>> + int time;
>>> + asm volatile("mftb %0" : "=r"(time)); // load from TBL register
>>> + PUSH(time);
>> This doesn't get TBL: on 64-bit implementations it gets all of TB. You'll
>> have to mask out the high half if you want to get just TBL. Or, you could
>> just use mftb (mfspr 268) on 64-bit systems, instead of the TBU dance that
>> you need on 32-bit systems.
> I wasn't aware that OpenBIOS supported 64-bit PowerPC. What if I change
> the type of the time variable to uint32_t. This type can only hold a
> 32-bit value, would the following code work on 64-bit PowerPC?
I don't know if it works (depends on the compiler implementation) but it
looks safer to explicitely mask the unneded bits in a new line between the
asm and PUSH.
> /* reads the lower timebase register ( -- tbl ) */
> static void get_tbl(void)
> uint32_t time;
> asm volatile("mftb %0" : "=r"(time)); // load from TBL register
> Also how would I test 64-bit PowerPC code in QEMU? If you could send the
> command-line needed that would help.
Look in openbios/include/arch/ppc/processor.h (and this is probably a
better place for these kind of helpers than qemu/init.c as these are PPC
specific not QEMU specific). However then you'd also need a way in Forth
to detect 64bit. Elsewhere in ppc/qemu CONFIG_PPC64 also seems to be used
and you may be able to test this in Forth, I've seen lines like:
[IFDEF] CONFIG_PPC64 " yes" [ELSE] " no" [THEN]
but not sure if this works. It seems to be cleaner to implement the tb@
function in C that returns the whole TB value instead of tbl@ and tbu@ and
export that to Forth so you don't need to handle arch differences such as
64bit in Forth.
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