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Kinetis K20 FlexNVM Read Issue

Question asked by JEFF STEVENS on Mar 13, 2013

I have an application running on a Kinetis K20 (MK20DX256VLQ10), with MQX 4.0, compiled with CW 10.3.  I have a weird issue with reading the data flash immediately after programming a virgin device.  To re-create, I do a full erase of the chip, program my application and data (which goes in the dataflash @ 0x10000000), then execute.  When I try to read the data flash I get a bus fault and am returned 0xFF for all values.  It doesn't matter how many times I reset the controller, it always fails.  However, all I have to do is stop the debugger and start a new debug session, and it magically works from there on out.  This is also true if I program the device and then run stand-alone.  If I program a virgin device and then try to power it up, the reads don't work.  I know this, because my graphics for the display are held in the data flash, so nothing appears on the screen when the reads aren't working.  However, I reconnect to the J-Link and reprogram, and everything runs fine from there on out. 


I have dumped the registers in both cases, and don't see anything that could explain this.  I did notice that the flash bank control registers (FMC_PFB0CR & FMC_PFB1CR) are set to 0x3002001F on the first program attempt, and then 0x30020000 after I stop and restart the debugger.  So, I'm wondering what the debugger is doing that is magically solving this issue.


I have attached a dump of the register contents of both a failed flash read and a good flash read.

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