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K22 DSPI in Slave Mode Sometimes Has Duplicate TX Bytes

Question asked by Chuck Horkin on Jan 2, 2018
Latest reply on Apr 16, 2018 by Hui_Ma

We're seeing an issue that only happens sometimes.  We are using the fsl_dspi.c/h modules with SPI in slave configuration.  We are transfering 4 bytes to the host and they should be: 0x79, 0xB8, 0xF8, 0x99.  However, sometimes, we actually get 0x79, 0x79, 0xB8, 0xF8.  Then, instead of getting an 0x99 on the next SPI transfer, we keep getting 0xF8.  It seems that there was some kind of error on the dspi_slave_transfer_callback_t(not kStatus_Success) and possibly an RX overflow.  We think we've tied this to SS behavior on the host side where the SS is held low longer, but we have no real explanation for why.

 

Has anyone had issues like this, or can point us in to how to proceed here?

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