Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Hardware and Software Partitioning of Operating Systems 197
For RTOS hardware IP, we start with an IP library of hardware components
consisting of the SoCDMMU, SoCLC, System-on-a-Chip Deadlock Detection
Unit (SoCDDU) [16] and Real-Time Unit (RTU) [20–24]. The SoCDMMU
and SoCLC were already described in the previous section; IP-generators for
the SoCDMMU and SoCLC can generate RTL Verilog code for almost any
configuration of the SoCDMMU and/or SoCLC desired [26, 27]. The
SoCDDU performs a novel parallel hardware deadlock detection based on
implementing deadlock searches on the resource allocation graph in hardware
[16]. It provides a very fast and very low area way of checking deadlock at
run-time with dedicated hardware. The SoCDDU reduces deadlock detection
time by 99% as compared to software.
Figure 15-10 shows a hardware RTOS unit called RTU [20–24]. The RTU
is a hardware operating system that moves the scheduling, inter-process
communication (IPC) such as semaphores as well as time management control
such as time ticks and delays from the software OS-kernel to hardware. The
RTU decreases the system overhead and can improve predictability and
response time by an order of magnitude. (This increased performance is due
to the reduced CPU load when the RTOS functionality is placed into
hardware.) The RTU also dramatically reduces the memory footprint of the
OS to consist of only a driver that communicates with the RTU. Thus, less
cache misses are seen when the RTU RTOS is used. The RTU also supports
task and semaphore creation and deletion, even dynamically at run time.
For RTOS software IP, we use the Atalanta RTOS, a shared-memory multiprocessor
real-time operating system developed at the Georgia Institute of
Technology [17]. This RTOS is specifically designed for supporting multiple
processors with large shared memory in which the RTOS is located and is
similar to many other small RTOSes. All PEs (currently supported are either
all MPC750 processors or all ARM9 processors) execute the same RTOS code
and share kernel structures, data and states of all tasks. Each PE, however,
runs its own task(s) designated by the user. Almost all software modules are