board/cogent/README.cma286 - u-boot - Git at Google

 CPU module revisions
 --------------------

 My cpu module has the model number "CMA286-60-990526-01". My motherboard
 has the model number "CMA102-32M-990526-01". These are both fairly old,
 and may not reflect current design. In particular, I can see from the
 Cogent web site that the CMA286 has been significantly redesigned - it
 now has on board RAM (4M), ethernet 10baseT PHY (on SCC2), 2 serial ports
 (SMC1 and SMC2), and 48pin DIN for the FEC (if present i.e. MPC860T), and
 also the EPROM is 512K.

 My CMA286-60 has none of this, and only 128K EPROM. In addition, the CPU
 clock is listed as 66MHz, whereas mine is 33.333MHz.

 Clocks
 ------

 Quote from my "CMA286 MPC860/821 User's Manual":

 "When setting up the Periodic Interrupt Timer (PIT), be aware that the
 CMA286 places the MPC860/821 in PLL X1 Mode. This means that we feed
 a 25MHz clock directly into the MPC860/821. This mode sets the divisor
 for the PIT to be 512. In addition, the Time Base Register (TMB)
 divisor is set to 16."

 I interpreted this information to mean that EXTCLK is 25MHz and that at
 power on reset, MODCK1=1 and MODCK2=0, which selects EXTCLK as the
 source for OSCCLK and PITRTCLK, sets RTDIV to 512 and sets MF (the
 multiplication factor) to 1 (I assume this is what they mean by X1
 mode above). MF=1 means the cpus internal clock runs at the same
 rate as EXTCLK i.e. 25MHz.

 Furthermore, since SCCR[TBS] (the Time Base Source selector bit in the
 System Clock and Reset Control register) is set in the cpu initialisation
 code, the TMBCLK source is forced to be GCLK2 and the TMBCLK prescale is
 forced to be 16. This results in TMBCLK=1562500.

 One problem - since PITRTCLK source is EXTCLK (25Mhz) and RTDIV is 512,
 PITRTCLK will be 48828.125 (huh?). Another quote from the MPC860 Users
 Manual:

 "When used by the real-time clock (RTC), the PITRTCLK source is first
 divided as determined by RTDIV, and then divided in the RTC circuits by
 either 8192 or 9600. Therefore, in order for the RTC to count in
 seconds, the clock source must satisfy:

 	(EXTCLK or OSCM) / [(4 or 512) x (8192 or 9600)] = 1

 The RTC will operate with other frequencies, but it will not count in
 units of seconds."

 Therefore, the internal RTC of the MPC860 is not going to count in
 seconds, so we must use the motherboard RTC (if we need a RTC).

 I presume this means that they do not provide a fixed oscillator for
 OSCM. The code in get_gclk_freq() assumes PITRTCLK source is OSCM,
 RTDIV is 4, and that OSCM/4 is 8192 (i.e. a ~32KHz oscillator). Since
 the CMA286-60 doesn't have this (at least mine doesn't) we can't use
 the code in get_gclk_freq().

 Finally, it appears that the internal clock in my CMA286-60 is actually
 33.333MHz. Which makes TMBCLK=2083312.5 (another huh?) and
 PITRTCLK=65103.515625 (bloody hell!).

 If anyone finds anything wrong with the stuff above, I would appreciate
 an email about it.

 Murray Jensen <Murray.Jensen@csiro.au>
 21-Aug-00
	CPU module revisions
	--------------------

	My cpu module has the model number "CMA286-60-990526-01". My motherboard
	has the model number "CMA102-32M-990526-01". These are both fairly old,
	and may not reflect current design. In particular, I can see from the
	Cogent web site that the CMA286 has been significantly redesigned - it
	now has on board RAM (4M), ethernet 10baseT PHY (on SCC2), 2 serial ports
	(SMC1 and SMC2), and 48pin DIN for the FEC (if present i.e. MPC860T), and
	also the EPROM is 512K.

	My CMA286-60 has none of this, and only 128K EPROM. In addition, the CPU
	clock is listed as 66MHz, whereas mine is 33.333MHz.

	Clocks
	------

	Quote from my "CMA286 MPC860/821 User's Manual":

	"When setting up the Periodic Interrupt Timer (PIT), be aware that the
	CMA286 places the MPC860/821 in PLL X1 Mode. This means that we feed
	a 25MHz clock directly into the MPC860/821. This mode sets the divisor
	for the PIT to be 512. In addition, the Time Base Register (TMB)
	divisor is set to 16."

	I interpreted this information to mean that EXTCLK is 25MHz and that at
	power on reset, MODCK1=1 and MODCK2=0, which selects EXTCLK as the
	source for OSCCLK and PITRTCLK, sets RTDIV to 512 and sets MF (the
	multiplication factor) to 1 (I assume this is what they mean by X1
	mode above). MF=1 means the cpus internal clock runs at the same
	rate as EXTCLK i.e. 25MHz.

	Furthermore, since SCCR[TBS] (the Time Base Source selector bit in the
	System Clock and Reset Control register) is set in the cpu initialisation
	code, the TMBCLK source is forced to be GCLK2 and the TMBCLK prescale is
	forced to be 16. This results in TMBCLK=1562500.

	One problem - since PITRTCLK source is EXTCLK (25Mhz) and RTDIV is 512,
	PITRTCLK will be 48828.125 (huh?). Another quote from the MPC860 Users
	Manual:

	"When used by the real-time clock (RTC), the PITRTCLK source is first
	divided as determined by RTDIV, and then divided in the RTC circuits by
	either 8192 or 9600. Therefore, in order for the RTC to count in
	seconds, the clock source must satisfy:

	(EXTCLK or OSCM) / [(4 or 512) x (8192 or 9600)] = 1

	The RTC will operate with other frequencies, but it will not count in
	units of seconds."

	Therefore, the internal RTC of the MPC860 is not going to count in
	seconds, so we must use the motherboard RTC (if we need a RTC).

	I presume this means that they do not provide a fixed oscillator for
	OSCM. The code in get_gclk_freq() assumes PITRTCLK source is OSCM,
	RTDIV is 4, and that OSCM/4 is 8192 (i.e. a ~32KHz oscillator). Since
	the CMA286-60 doesn't have this (at least mine doesn't) we can't use
	the code in get_gclk_freq().

	Finally, it appears that the internal clock in my CMA286-60 is actually
	33.333MHz. Which makes TMBCLK=2083312.5 (another huh?) and
	PITRTCLK=65103.515625 (bloody hell!).

	If anyone finds anything wrong with the stuff above, I would appreciate
	an email about it.

	Murray Jensen <Murray.Jensen@csiro.au>
	21-Aug-00