Changes

This is, typically, a few trace records for each eMMC access. Stress tests have verified that logging an eMMC access (functions <code>mmc_start_request() </code> and <code>mmc_request_done() </code> with related data) requires about 416 trace records in the PowerTrace memory and these accesses occur on average every 4 mSec. This corresponds to approximately 1GB/416 = 2.5 million eMMC logs, or approximately 10,000 seconds (2h45min) for each gigabyte of trace storage. The PowerTrace family provides either 10 million eMMC logs (11h) for a 4GB PowerTrace or 20 million (22h) for an 8GB module.By extending the trace duration with trace streaming, the limit becomes the size of the computer hard-disk/SSD or the TRACE32 limit which is 1 Tera-frame, i.e., 2.5 billion eMMC logs (over 100 days!). The trace data can be filtered and saved on disk, and then converted into a more suitable format for analysis using a TRACE32 script (PRACTICE script), Python script, or an external conversion program. For example, the trace shown above can be converted into the format shown below, which is more suitable for importing into specific eMMC analysis tools: <pre class="workstation-terminal">24.228827980 mmc_start_req_cmd: host=mmc1 CMD25 arg=01620910 flags=000000B5 blksz=00000200 blks=0000001024.231239610 mmc_request_done: host=mmc1 CMD25 err=00000000 resp1=00000900 resp2=00000000</pre> These tools perform a complete analysis of the eMMC device application accesses, in terms of addresses accessed, frequency and access methods. The end goal is to calculate the Write Amplification Factor (WAF) seen by the eMMC (or by any other managed-NAND block device). WAF is defined as the ratio of physical data written onto the NAND and the data written by the host. When the host writes logical sectors of the eMMC, the internal eMMC controller erases and re-programs physical pages of the NAND device. This could cause a management overhead. Large sequential writes aligned to physical page boundaries typically result in minimal overhead and optimal NAND write activity (WAF=~1). Small chunks of random writes could result in a higher overhead (WAF>>1). This becomes important when considering the life of the raw-NAND memory inside the eMMC, which has a finite number of Program/Erase cycles. See the example below: TBD To estimate the WAF for any particular eMMC device, and hence its expected lifetime on your application, you can capture the log file of the activity. Once a log is obtained, it's recommended to contact your eMMC vendor to get more information about the log analysis tools required for analyzing the specific eMMC product.