1/2Application AdvisoryTitleOptimization of eFuse Programming forESP32 / ESP32-C3 / ESP32-S2 / ESP32-S3 Series of ChipsIssue date2022/09/22Advisory NumberAR2022-006Serial NumberNAVersionv1.0Issue SummaryIf secure boot v1, secure boot v2, and/or flash encryption are used, and there areno corresponding keys burned in eFuse, the bootloader will generate the key andburn it to the corresponding eFuse BLOCK. It was identified that there is a verysmall probability of failure in some cases where eFuse bits might not be burnedfrom 0 to 1.For secure boot v1 and secure boot v2, if the eFuse key is not correct, theverification of bootloader will fail, and the system will not be started up normally.For the IDF versions older than v4.4.2, v4.3.3, v4.2.4, there is no eFuse datavalidation after burning in bootloader.The issue has been investigated. Due to the use of different programmingenvironments, the following possible causes have been identified of eFuse bits notbeing flashed correctly:1. The power-up and power-down time of eFuse time settings is not configuredappropriately.2. Some eFuse bits are not easily fused by a single program action.In order to decrease the failure rate, the following updates have been introduced inESP-IDF:1. Updated the eFuse time settings configuration for power-up and power-down.2. Introduced the option to validate the eFuse data after burning and re-burning.Fixed/Patched Versions for ESP-IDFThe above-mentioned updates have been included in the ESP-IDF v5.0-beta1,v4.4.2, v4.3.3, v4.2.4 releases and will be present in the newer versions.The detailed commits in the ESP-IDF branches are as follows: 2/2Release/V4.2: b85c0ec35210c2f15d69b6ec79b662df9ba75392Release/V4.3: 9bbe2fc041c5e0bb7ecaf8d1b5e782d0ac2e4649Release/V4.4: 6382b51bfbaf6a17a709601dbe3b8f9c6ea4f0dcRelease/V5.0: 2ce6c78af44e5fbeede7eb5e74c55e4958d81dc3Recommendations for Espressif Users If your application uses secure boot v1, secure boot v2 or flash encryption as wellas uses the bootloader to generate the key and burn it to the corresponding eFuseBLOCK, it is recommended that you update to the latest stable IDF release versionthat includes the above-mentioned updates.Although, very few reports regarding the issue in question have been received fromESP32 ECO, V3 customers, it is still recommended that you use the latest stableIDF release version with other ESP32 series of chips, e.g. ESP32-C3, ESP32-S2and ESP32-S3.