External Memory Interface Handbook Volume 3: Reference Material

ID 683841
Date 7/24/2019
Document Table of Contents

2.12.1. Method for Initiating a User-requested Reset

Step 1 - Precondition

Before asserting local_reset_req, user logic must ensure that the local_reset_done signal is high.

As part of the device power-on sequence, the local_reset_done signal automatically transitions to high upon the completion of the interface calibration sequence, regardless of whether calibration is successful or not.

Note: When targeting a group of interfaces that share the same core clocks, user logic must ensure that the local_reset_done signal of every interface is high.

Step 2 - Reset Request

After the pre-condition is satisfied, user logic can send a reset request by driving the local_cal_req signal from low to high and then low again (that is, by sending a pulse of 1).

  • The 0-to-1 and 1-to-0 transitions need not happen in relation to any clock edges (that is, they can occur asynchronously); however, the pulse must meet a minimum pulse width of at least 2 EMIF core clock cycles. For example, if the emif_usr_clk has a period of 4ns, then the local_reset_req pulse must last at least 8ns (that is, two emif_usr_clk periods).
  • The reset request is considered complete only after the 1-to-0 transition. The EMIF IP does not initiate the reset sequence when the local_reset_req is simply held high.
  • Additional pulses to local_reset_req are ignored until the reset sequence is completed.

Optional - Detecting local_reset_done deassertion and assertion

If you want, you can monitor the status of the local_reset_done signal to to explicitly detect the status of the reset sequence.

  • After the EMIF IP receives a reset request, it deasserts the local_reset_done signal. After initial power-up calibration, local_reset_done is de-asserted only in response to a user-requested reset. The reset sequence is imminent when local_reset_done has transitioned to low, although the exact timing depends on the current state of the I/O Subsystem Manager (IOSSM). As part of the EMIF reset sequence, the core reset signal (emif_usr_reset_n, afi_reset_n) is driven low. Do not use a register reset by the core reset signal to sample local_reset_done.
  • After the reset sequence has completed, local_reset_done is driven high again. local_reset_done being driven high indicates the completion of the reset sequence and the readiness to accept a new reset request; however, it does not imply that calibration was successful or that the hard memory controller is ready to accept requests. For these purposes, user logic must check signals such as afi_cal_success, afi_cal_fail, and amm_ready.

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