Using the Process Manager Userspace Application

The Process Manager application is an interactive, screen-based application for viewing and controlling the applications installed on a Tock board. This guide will help you install it and walk you through its features.

Tock Kernel Image

If you haven't already, install the tutorials/nrf52840dk-dynamic-apps-and-policies kernel on your board.

$ cd tock/boards/tutorials/nrf52840dk-dynamic-apps-and-policies
$ make install

If you are using a different hardware platform, be sure to follow the pre-setup steps in the overview before proceeding.

Install the Process Manager Application

You can install the Process Manager app like any other Tock application. You can find it in libtock-c/examples/tutorials/dynamic-apps-and-policies/process_manager.

$ cd libtock-c/examples/tutorials/dynamic-apps-and-policies/process_manager
$ make
$ tockloader install

Exploring with the Process Manager Application

When the Tock kernel is running the Process Manager should be shown on the screen:

Process Manager App

Interact with the application using the buttons:

┌────────────────────────────────────────────────────────────────────┐
│                                                                    │
│                                                LED1 ☐ ☐ LED2       │
│                                                LED3 ☐ ☐ LED4       │
│           ┌────────────────┐                                       │
│           │                │                                        ╲
├───┐       │                │                                         │
│USB│       │     Screen     │                                         │
├───┘       │                │                      ┌─┐  ┌─┐           │
│           │                │                  Up--│O│  │O│           │
│           └────────────────┘                      └─┘1 └─┘2          │
│                                                   ┌─┐  ┌─┐           │
│                                             Down--│O│  │O│--Enter   ╱
│                                                   └─┘3 └─┘4        │
└────────────────────────────────────────────────────────────────────┘

nRF52840dk Button Number	Action
1	Up
2	unused
3	Down
4	Enter

Process Manager supports inspecting and controlling existing processes and installing new applications.

Viewing Active Processes

Scroll to "Inspect Processes" and hit enter (BUTTON 4). This will list all active processes (including the Process Manager application). You can scroll up and down to look through all installed applications.

Details on a Specific Process

Scroll to a desired application such that it is highlighted on the screen. Press the enter button (BUTTON 4) to select it. You will now see a list of details about that application.

Entry	Name	Description
PID	`ProcessId`	The ProcessId is the runtime identifier for the process. Every time a process starts it gets a new ProcessId. All process IDs must be unique.
ShortID	`ShortId`	The ShortId is the fixed identifier for a specific application. Each Tock kernel uses a policy for determining the ShortId. This identifier is persistent across reboots and restarts.
Timeslices Exp	Expired Timeslices	The number of times the process exceeded its timeslice and was pre-empted by the kernel.
Syscall Count	Number of System Calls	How many system calls the process has made.
Restart Count	Number of Restarts	How many times the process has been restarted, either manually or after a crash.
State	Process State	The current state of the process. Most likely `Yielded` because the Process Manager must be running to update the screen.
State Control	Change the Process State	Control the process by changing its state. See below.

Controlling a Specific Process

The Process Manager application also enables you to control the execution of a process. Highlight State Control and press enter. With the action field highlighted, press enter to scroll through the available actions:

Operation	Description
Start	Resume running a stopped process.
Stop	Halt a running process such that it is no longer scheduled to run.
Fault	Cause a process to crash and have the kernel run the process's fault handler.
Terminate	Stop a process and have its resources released.
Boot	Start running a terminated or never started process.

Choose the action for the selected process and then press down to highlight OK, and then enter to perform that action.

Not all actions are valid from all process states. In particular, boot is only valid when the process is terminated, and start and stop are only valid when the process is running or yielded.

Now that you have the Process Manager running, let's take advantage of the app loading functionality in the next section.

The Tock Book