[syslinux] "Tick-counting" vs "Tick-less" timekeeping issues on VMs emulating BIOS PCs

[Patrick Masotta]

> 

> There are quite a few; primarily we simply cannot make lwIP
> (lpxelinux.0) work without it.  However, pxelinux.0 should not depend on
> this.


I'm finding most of the problems on lpxelinux.0 

>
>Now, tickful timekeeping is wasteful, but this is a bootloader, and
>functionality is the main concern.  The "tickless" version still
>depended on the BIOS tick.
>

Not really, a virtual environment can easily emulate the BIOS_timer	at 0x046C
but it has problems emulating a "real" timer interrupt to be hooked...
That's the real problem.

Just testing I have replaced the timing functions 


#define BIOS_timer	0x046C	// Timer ticks 
typedef uint32_t jiffies_t;
extern volatile jiffies_t __jiffies, __ms_timer;
static inline jiffies_t jiffies(void)
{
return (*(volatile uint32_t *)BIOS_timer);

}

typedef uint32_t mstime_t;
typedef int32_t  mstimediff_t;
static inline mstime_t ms_timer(void)
{
return ((*(volatile uint32_t *)BIOS_timer) * 55);

}

lpxelinux.0 hangs while legacy works OK.

I think we should not depend on hoking timer interrupts if we want to be compatible with virtual environments.

Best,
Patrick