mcf54415 ddr2 clock speed

[angelo_d]

Hi all,

have a queston on ddr2 clock speed on mcf54415 custom board.

What i actually so is :

- pll setup, i have

  fref = 30Mhz,

  refdiv = 0 (refdiv_divider = 1),

  cpu_clock configured to 240Mhz

  vco clock fixed at cpu_clock * 2,

  bus_clock at cpu_clock / 2

- ddr2 (128MB) init / setup

- memtest, passes all 128MB

- finally, DDR2 clock checked by scope, i see a syn at abt 240Mhz.

Strangely, since i set that that ddr2 clock must come from VCO, with

    /* use vco instead of cpu 2x clock for ddr clock */
    move.l    #MISCCR2, %a1
    move.w    #0xe01d, (%a1)
    /* use cpu clock */
    /* move.w    #0xa01d, (%a1) */

should i expect 480Mhz as ddr2 clock and 240 only if i set ddr2 clock coming from cpu clock ?

Thanks

angelo

[angelo_d]

many thanks !

[TomE]

The Data Sheet gives a min/max range for SD_CLK from 100 to 250MHz.

That wasn't what you were asking, but the programming you have seems to be achieving that goal.

The diagram in "Figure 8-1. Device Clock Connections" and accompanying text in the Reference Manual is all you get. The description of "MISCCR2[DDR2CLK]" might help. It looks like the DDR module takes a double-frequency clock as input.

Tom