[U-Boot-Users] mpc8245 timer

[U-Boot-Users] mpc8245 timer

[DeLaGarza, Robert]

The following code appears in u-boot-0.3.0/cpu/mpc824x/cpu.c

/*
 * Get timebase clock frequency (like cpu_clk in Hz)
 * This is the sys_logic_clk (memory bus) divided by 4
 */
unsigned long get_tbclk (void)
{
	return ((get_bus_freq (0) + 2L) / 4L);
}


However, in Table 11-11 of the _MPC8245 Integrated Processor User's Manual_,
there is the statement "The timers operate at 1/8 the speed of the SDRAM_CLK signal."

Should the divisor in get_tbclk( ) be 8L for the MPC8245?

(I know there are several '8245 and '8241 boards using PPCBoot and/or U-Boot, so my
guess is that the manual is wrong, but I didn't see anything in the errata about this.)

[U-Boot-Users] mpc8245 timer

[Wolfgang Denk]

In message <01C302F0.40E40DC0.robdlg@att.net> you wrote:
> The following code appears in u-boot-0.3.0/cpu/mpc824x/cpu.c
> 
> /*
>  * Get timebase clock frequency (like cpu_clk in Hz)
>  * This is the sys_logic_clk (memory bus) divided by 4
>  */
> unsigned long get_tbclk (void)
> {
> 	return ((get_bus_freq (0) + 2L) / 4L);
> }

This was designed for MPC8240 systems; where the  timebase  registers
are  incremented  once  for  every  for sys_logic_clk cycles. And all
systems I've seen so far used sys_logic_clk = 2 x PCI bus frequency.

> 
> However, in Table 11-11 of the _MPC8245 Integrated Processor User's Manual_,
> there is the statement "The timers operate at 1/8 the speed of the SDRAM_CLK signal."
> 
> Should the divisor in get_tbclk( ) be 8L for the MPC8245?

You can easily try it out: how long does "sleep 10" sleep on your system?


Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
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But you imprison those who employ it privately.
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[U-Boot-Users] mpc8245 timer

[DeLaGarza, Robert]

On Tuesday, April 15, 2003 2:00 AM, Wolfgang Denk [SMTP:wd at denx.de] wrote:
> In message <01C302F0.40E40DC0.robdlg@att.net> you wrote:
> > 
> > ...in Table 11-11 of the _MPC8245 Integrated Processor User's Manual_,
> > there is the statement "The timers operate at 1/8 the speed of the SDRAM_CLK signal."
> > 
> > Should the divisor in get_tbclk( ) be 8L for the MPC8245?
> 
> You can easily try it out: how long does "sleep 10" sleep on your system?


Yes--thanks.  I tested "sleep 10" on both our '8245 reference board (an Artis Microsystems
SBC-A3000) and our own custom '8241 board.  In both cases, the sleep interval was correct.

Thus, the divisor in get_tbclk( ) appears to be fine.  I will disregard Table 11-11, as it does not
seem to apply here.