MPC8360 DDR Specific FAQs

Document created by Omar Cruz Employee on Jul 31, 2012
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For MPC8360, is any way that the CPU can read and write the full 72-bit wide DDR memory bus, bypassing the ECC logic? I want to know if the memory controller can be configured for the 72-bit wide DDR memory bus to bypass the ECC logic.

It is not possible to bypass the ECC and read/write using full 72-bit wide bus. The controller uses the last byte lane to generate ECC info and cannot be bypassed.

For MPC8360 DDR SDRAM refresh, can you please advise how to "exactly" calculate the appropriate value of [REFINT] if such worst case scenario in which refresh command issue timing is postponed is taken into account?

The refresh interval should be set as high as allowable by the DRAM specifications. This should be calculated by using tREFI in the DRAM specifications, which may depend upon the operating temperature of the DRAM. In addition, to allow a memory transaction in progress to be completed when the refresh interval is reached and not violating the device refresh period, set the REFINT value to a value less than that calculated by using tREFI. The value selected for REFINT could be larger than tREFI if the DDR_SDRAM_CFG[NUM_PR] has a value higher than 1. To calculate the max possible value when DDR_SDRAM_CFG[NUM_PR] is higher than 1, use the following formula: (tREFI/clk period) x (NUM_PR) = REFINT

A timing tDISKEW (skew between MDQS and MDQ) is depicted in DDR2 and DDR3 SDRAM Interface Input Timing Diagram in MPC8360 Hardware spec. For measuring tDISKEW, please instruct me from which point of the MDQS waveform and to which point of MDQ waveform should be measured?

For measuring MDQS, it should be at the cross point. For case of MDQ it is derated to the VREF.

Why does MCK to MDQS Skew tDDKHMH has such a high value of +/-525ps for DDR3 800M data rate for MPC8360? I am afraid that write-leveling can NOT remove all internal MCK to MDQS skew from tDDKHMH. Can you please let me know how much internal skew will be removed after write-leveling?

tDDKHMH value of +/-525ps for MPC8360 part is a conservative value in the HW spec. For DDR3 with write leveling enabled, this AC timing parameter would be a non-factor.

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