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+# Blocking calls handling
+
+## Use case
+
+1. The process wants to start a blocking operation (`sleep`, disk operation...).
+   Via an interrupt, it calls the corresponding function from the driver.
+2. The driver launches the operation and keeps the pid of the process.
+3. The driver calls `scheduler_wait_blocking`, with a callback to cancel the
+   operation as parameter (see below). The process is stopped and marked as
+   `WAITING`.
+4. When the operation completes (usually via a hardware interrupt), the driver
+   calls `scheduler_wake_blocking` with the pid and a return value as parameter.
+   The process is marked as `READY`.  Its saved value for `A` is set to the
+   return value.
+5. The execution of the process can restart from the line after the call to
+   `scheduler_wait_blocking`. The result code is the return value of
+   `scheduler_wait_blocking`.
+
+## Scheduler
+
+The scheduler only launches processes in the `READY` state. If none are
+available, it runs `HLT`.
+
+## Process end
+
+If a process is killed while `WAITING`, the scheduler calls the callback with
+the pid as parameter.