HJZ

TIL - gitsha with dirty

Wed, 26 Nov 2025 00:00:00 +0000

git describe --always --dirty --match=''

This command return the gitsha of HEAD, in short form, and attaches -dirty suffix if there is change in tracked files. 7e68a98, 7e68a98-dirty. Staged files is also considered as dirty.

The --match="" avoid matching to any nearby git tags, and always return the gitsha.

This is helpful sometime in build system for tracking application version.

Cortext M chip reset behaviour

Sun, 06 Apr 2025 00:00:00 +0000

Upon power-on reset, the Cortex-M processor’s initial actions involve accessing the vector table • The core first reads the initial Stack Pointer (SP) from the first entry of the vector table (at address 0x00000000) • Then, the core reads the start Program Counter (PC), which is the reset vector, from the second entry of the vector table (at address 0x00000004) The Link Register (LR) is also set to 0xFFFFFFFF • Execution then begins at the address pointed to by the reset vector.

Goose on weekend side projects

Mon, 10 Mar 2025 00:00:00 +0000

I spent some of my limited spare time between childcare duties working on a project: creating llvm-binary-releases using Goose. The goal was straightforward: take an LLVM release package, extract the specific clang tool binary I needed, and produce a new platform/OS-specific release. I planned to set up a hermit package for clang-format because finding pre-built clang binaries is surprisingly difficult. While native package managers are available, they tend to complicate dependency management in build systems, so I decided to solve the problem myself.

Dev notes from Feb 2025

Fri, 28 Feb 2025 00:00:00 +0000

Git performance tracing

I noticed that some git commands, especially git status, were taking a long time to execute. Since it’s tied to my command prompt, this also slowed down my prompt. By using GIT_TRACE=1, I could see what git was doing. The issue was that the repository had too many submodules, causing git status to run on each one, which took time.

$ GIT_TRACE=1 git status
14:40:25.548035 git.c:476 trace: built-in: git status
14:40:25.550695 run-command.c:667 trace: run_command: cd themes/hello-friend-ng; unset GIT_PREFIX; GIT_DIR=.git git status --porcelain=2
14:40:25.550763 run-command.c:759 trace: start_command: /opt/homebrew/opt/git/libexec/git-core/git status --porcelain=2
14:40:25.557470 git.c:476 trace: built-in: git status --porcelain=2
On branch main
Your branch is up to date with 'origin/main'.

14:40:25.567125 run-command.c:667 trace: run_command: GIT_INDEX_FILE=.git/index git submodule summary --cached --for-status --summary-limit -1 HEAD
14:40:25.567200 run-command.c:759 trace: start_command: /opt/homebrew/opt/git/libexec/git-core/git submodule summary --cached --for-status --summary-limit -1 HEAD
14:40:25.573148 git.c:769 trace: exec: git-submodule summary --cached --for-status --summary-limit -1 HEAD
...

Fish shell performance tracing

Similarly, the fish shell has a profiling feature:

Trigger DFU via USB on nRF52840 Dongle

Sat, 06 Apr 2024 00:00:00 +0000

The NRF5280 dongle is a great embedded development platform, especially for hobbyist project or quick prototyping. There is also a very similar product from Make Diary with slightly different PCBA layout. It is generally a decent utility tool for BLE related work. These functionality can all be done out of box with the nrf desktop tool without doing any programming.

There are plenty of blog post on this already that covers introductory programming with the nordic part. But one interesting feature that I run into while working with this dongle was how to trigger DFU programming quickly.

About

Tue, 28 Sep 2021 21:33:00 -0400

Hello, I’m Hantian James Zhao. I’m a Embedded/Firmware Software Engineer. I have spend most of my career writing software that runs on embedded hardwares. I am Canadian-Chinese, complete fluent in English, conversational in Chinese, and barely survivable French and Japanese. My current home is Somerville, Massachusetts.

My resume

Tue, 28 Sep 2021 21:33:00 -0400

Past employments

Google Geo Sustainability|Senior Software Engineer

LTE modem product bring up, integration, field deployment for protoype studies in 10+ sites over US
Redesigned and migrated FW project to GN build system, improve build time and eliminate flakly builds
Implemented python host tools framework for developers and field ops’ speeding up daily operations
Automating github CI framework with on device HW test

Verily Life Sciences|Senior Firmware Engineer / Tech Lead

Firmware Lead of Verily Patch Class 1 med device, taking it from start to pilot
Drove product Bluetooth SIG certification and FDA 510K certification
Manage cross functional team communication and product schedules
Technical mentor-ship of junior team members
Oversaw FW release process and implementation of release infrastructure

Verily Life Sciences|Firmware Engineer

Enabled HW factory manufacturing flow in China
Achieved multiple internal/external user studies and GA launch
Own multiple core system components
Published python host tools to internal and external users
Bring up and maintain BLE communication stack on Nordic NRF528xx

Square|Android Platform Engineer

Developed custom Android Platform for new POS register
Designed and Implemented WIFI + USB log monitoring services for telemetry purpose
Debugged and optimized Android WIFI stack
Implemented over the air system upgrade components

Square|Embedded Software Engineer

Developed firmware and help ship 2 Square credit card reader products
Build up and maintained a CI/CD on-device HW test infrastructure
Implemented a USB stack on Freescale Kinetis MCUs
Design and Implemented battery management and power control logic for Square card readers
Implement JTAG/GDB/OpenOCD support for new custom silicon

Nvidia|Android Platform Software Engineer

Developed hardware feature verification tests of Tegra4 crypto engine
Maintained and developed Trustzone secure OS on Tegra Android
Maintained and developed Widevine, HDCP key management in Android
Designed and developed Trustzone secure OS build flow within Android
Work with OpenOCD, open source project, to bring a kernel debugger compatible with Tegra 3 devices