seL4 Timer tutorial
This tutorial demonstrates how to set up and use a basic timer driver.
You’ll observe that the things you’ve already covered in the other tutorials are already filled out and you don’t have to repeat them: in much the same way, we won’t be repeating conceptual explanations on this page, if they were covered by a previous tutorial in the series.
- Allocate a notification object.
- Set up a timer provided by seL4 libs.
seL4_libsfunctions to manipulate timer and handle interrupts.
First, build and run the tutorial:
# create a build directory mkdir build_hello_timer cd build_hello_timer # initialise your build directory ../init --plat pc99 --tut hello-timer # build it ninja # run it in qemu ./simulate
Before you have done any tasks, when running the tutorial should show the timer and timer client waking up, then a cap fault is triggered due to incomplete code:
main: hello world timer client: hey hey hey main: got a message from 0x61 to sleep 2 seconds Caught cap fault in send phase at address 0x0 while trying to handle: vm fault on data at address 0x0 with status 0x4 in thread 0xffaf7900 "hello-timer" at address 0x804841a With stack: 0x80bc880: 0x806838c 0x80bc884: 0x61 0x80bc888: 0x2 0x80bc88c: 0x80482ff 0x80bc890: 0x20 0x80bc894: 0x0 0x80bc898: 0x0 0x80bc89c: 0x0 0x80bc8a0: 0x80bc8c0 0x80bc8a4: 0x80bc8d0 0x80bc8a8: 0x80be010 0x80bc8ac: 0x7 0x80bc8b0: 0x0 0x80bc8b4: 0x0 0x80bc8b8: 0x0 0x80bc8bc: 0x10000000 QEMU: Terminated
TASK in the
apps/hello-timer directory for
The first task is to allocate a notification object to receive interrupts on. The output will not change as a result of completing this task.
Use our library function
initialise a timer driver. Assign it to the
timer global variable.
After this change, the server will no longer fault and the output will look something like this:
Searching for ACPI_SIG_RSDP Parsing ACPI tables timer client: hey hey hey email@example.com:362 Requested fsb delivery, but timer0 does not support main: hello world main: got a message from 0x61 to sleep 2 seconds timer client wakes up: got the current timer tick: 17299121
While at the end of the previous task the tutorial appears to be working, the main thread replies immediately to the client and doesn’t wait at all.
Consequently, the final task is to interact with the timer: set a timeout, wait for an interrupt on the created notification, and handle it.
After this task is completed you should see a 2 second wait between the message being sent and received.