SPI flash data logger library exception on read after a buffer overwrite

smadhavan · May 10, 2018, 3:35pm

The library SpiFlashLogger throws an exception when processing a read, when the oldest log has been intentionally overwritten, due to the log being full.

In _getObject() there is a check that the object marker is as expected. However after the object start code positions have been gathered by _getObjectsStartCodesForSector() and before the object is read by _getObject(), it is possible for the sector to be overwritten, when the buffer if full.

In this case, the object start codes will be out of date and a exception is thrown.

Proposed solution:

In _getObject() replace this:
if (marker != SPIFLASHLOGGER_OBJECT_MARKER) {
throw "Error, marker not found at " + pos;
}
with:
if (marker != SPIFLASHLOGGER_OBJECT_MARKER) {
return null;
}

In function read(), within readObj(), test obj for null and return cont():
if (obj == null) {
return cont();
}

smadhavan · May 11, 2018, 7:18am

The following code reproduces the problem:

// ------------------------------------------------------------------------
#require “Serializer.class.nut:1.0.0”
#require “SPIFlashLogger.device.lib.nut:2.2.0”

logger <- SPIFlashLogger(0, 4096*4);

function writeFlash() {
logger.write(blob(1000));
imp.wakeup(0.1, writeFlash);
}

function readFlash() {
logger.read(
// For each object in the logs (onData)
function(dataPoint, address, next) {
logger.erase(address);
imp.wakeup(0.5, next);
},

    // All finished (onFinish)
    function() { 
        imp.wakeup(0.5, readFlash );
    }
);

}

logger.eraseAll(false);
logger.write(blob(4000*4));
writeFlash();
readFlash();
// ------------------------------------------------------------------------

And this results in: