diff options
Diffstat (limited to 'include/hw/timer/armv7m_systick.h')
| -rw-r--r-- | include/hw/timer/armv7m_systick.h | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/include/hw/timer/armv7m_systick.h b/include/hw/timer/armv7m_systick.h index cca04defd8..25e5ceacc8 100644 --- a/include/hw/timer/armv7m_systick.h +++ b/include/hw/timer/armv7m_systick.h @@ -31,4 +31,26 @@ typedef struct SysTickState { qemu_irq irq; } SysTickState; +/* + * Multiplication factor to convert from system clock ticks to qemu timer + * ticks. This should be set (by board code, usually) to a value + * equal to NANOSECONDS_PER_SECOND / frq, where frq is the clock frequency + * in Hz of the CPU. + * + * This value is used by the systick device when it is running in + * its "use the CPU clock" mode (ie when SYST_CSR.CLKSOURCE == 1) to + * set how fast the timer should tick. + * + * TODO: we should refactor this so that rather than using a global + * we use a device property or something similar. This is complicated + * because (a) the property would need to be plumbed through from the + * board code down through various layers to the systick device + * and (b) the property needs to be modifiable after realize, because + * the stellaris board uses this to implement the behaviour where the + * guest can reprogram the PLL registers to downclock the CPU, and the + * systick device needs to react accordingly. Possibly this should + * be deferred until we have a good API for modelling clock trees. + */ +extern int system_clock_scale; + #endif |