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FMC synchronous non-multiplexed PSRAM clock spikes when writing

Question asked by leinad on Sep 13, 2017



We are using FMC for communication with FPGA. FPGA has memory-mapped periphery implemented in compatible mode for synchronous non/multiplexed PSRAM/NOR.

We are facing problem with misinterpreted spikes/cut pulses in CLK signal at higher frequencies (see pictures below).

FMC clock on oscilloscope


These are screenshots of ILA blocks (logic analyzers in FPGA). It shows how bus is interpreted and seen by logic in FPGA.ILA FMC bus


ILA FMC bus detail


It seems that these "cut" CLK pulses shows before NWE signal is toogled. Also this only happens when we write data...not when reading from memory.


It is can be fw/hw bug or it is a feature of MCU?


Used MCU: STM32F767ZI


FMC configuration

FMC CLK 6MHz (FMC div 16), continuous

    Timing.AddressSetupTime = 15;
    Timing.AddressHoldTime = 15;
    Timing.DataSetupTime = 255;
    Timing.BusTurnAroundDuration = 15;
    Timing.CLKDivision = 16;
    Timing.DataLatency = 2;
    Timing.AccessMode = FMC_ACCESS_MODE_A;

Memory type PSRAM

Address 24bits

Data 16 bits

Clock Burst Read Write

Address valid signal enabled

NWAIT signal enabled