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Diffstat (limited to 'board/cogent/README.cma286')
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diff --git a/board/cogent/README.cma286 b/board/cogent/README.cma286 deleted file mode 100644 index 0345feae00..0000000000 --- a/board/cogent/README.cma286 +++ /dev/null @@ -1,69 +0,0 @@ -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 |