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@cmst.csiro.au> 21-Aug-00