BlackBerry 10 OS for ARMv7 Cortex A-8 and A-9 Processors
We'll show you how to set up BlackBerry 10 OS for boards that support ARMv7 Cortex A-8 and Cortex A-9 processors.
The support for ARMv7 architecture processors (Cortex) is provided by:
- The libstartup.a library, which initializes the ARMv7 MMU features
- The QNX Neutrino microkernel, procnto , which uses the ARMv7 MMU
ARMv7 has two options for handling single-precision floating point: NEON and VFPv3. When ARMv7 processors boot, libstartup detects the presence of the NEON engine and Floating-Point Unit (FPU), and sets the CPU flags accordingly.
$QNX_TARGET/armle-v7 provides binaries that run only on ARMv7 processors, and that were built with options optimized for the ARMv7 architecture:
- They use only ARMv7 instructions.
- They use VFPv3-d16 instructions for floating-point operations.
The kernels are named procnto and procnto-instr because there's a single variant that supports only ARMv7 processors.
Behavior of shm_ctl()
The procnto microkernel for ARMv7 takes advantage of the ARMv7 MMU's physically-tagged cache to remove the 32 MB address space restriction imposed by the earlier ARM MMU architecture; the per-process address space is now 2 GB.
The microkernel doesn't implement the ARM-specific global memory region implemented by earlier microkernels for ARM. This means that shm_ctl() no longer has any ARM-specific special behavior:
- Objects created with shm_ctl() are always mapped into each process address space. These mappings are inherited across a fork() function.
- SHMCTL_GLOBAL is ignored, since all mappings are placed in the per-process address space.
- SHMCTL_PRIV and SHMCTL_LOWERPROT are ignored. All mappings are created in the per-process address space with user mode access protections.
Runtime features for a processor are indicated by the following flags found within the flags member of the cpuinfo area of the system page:
- A VFP unit is present. The VFP functionality support is enabled when the startup program detects the presence of VFP hardware and sets the system page CPU_FLAG_FPU flag.
- A NEON unit is present.
- An iWMMX2 coprocessor is present.
- The CPU implements the ARMv7 architecture.
- The target is running multiple processors.
NEON is optional in ARMv7 and may not be implemented by all processor implementations. The ARM_CPU_FLAG_NEON flag is set if a NEON unit is present.
Using ARMv7 instructions
By default, qcc provides only ARMv7 instructions.
The ARMv7 architecture introduces a number of new instructions that may provide performance benefits for certain code. For example, DSP algorithms can take advantage of the new media instructions.
For ARMv7, the -Vgcc_ntoarmv7le option makes qcc use ARMv7 instructions and generate VFPv3-d16 code for floating point. This is the default for the ARMle-v7 variant. This means that the ARMle-v7 variant can run only on ARMv7 targets with a VFP unit; it's been compiled for VFPv3-d16, which is the lowest common denominator for VFP. For example, if you use a VFPv3-d32 FPU, your compiled code will use only half of the available double-precision registers.
Last modified: 2015-03-31