The timer and entropy seed CSRs will, by design, return different
values each time they are read.
Add the missing volatile qualifiers on the inline assembly to prevent
gcc from assuming that repeated invocations may be elided.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
The Zicntr extension defines an unprivileged wall-clock time CSR that
roughly matches the behaviour of an invariant TSC on x86. The nominal
frequency of this timer may be read from the "timebase-frequency"
property of the CPU node in the device tree.
Add a timer source using RDTIME to provide implementations of udelay()
and currticks(), modelled on the existing RDTSC-based timer for x86.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
