The official git repository for OSD-Contiki, the open source OS for the Internet of Things
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OR-ing an offset to a base address instead of adding it is dangerous because it can only work if the base address is aligned enough for the offset. Moreover, if the base address or the offset has a value unknown at compile time, then the assembly instructions dedicated to 'base + offset' addressing on most CPUs can't be emitted by the compiler because this would require the alignment of the base address against the offset to be known in order to optimize 'base | offset' into 'base + offset'. In that case, the compiler has to emit more instructions in order to compute 'base | offset' on most CPUs, e.g. on ARM, which means larger binary size and slower execution. Hence, replace all occurrences of 'base | offset' with 'base + offset'. This must become a coding rule. Here are the results for the cc2538-demo example: - Compilation of uart_init(): * before: REG(regs->base | UART_CC) = 0; 200b78: f446 637c orr.w r3, r6, #4032 ; 0xfc0 200b7c: f043 0308 orr.w r3, r3, #8 200b80: 2200 movs r2, #0 200b82: 601a str r2, [r3, #0] * now: REG(regs->base + UART_CC) = 0; 200b7a: 2300 movs r3, #0 200b7c: f8c4 3fc8 str.w r3, [r4, #4040] ; 0xfc8 - Size of the .text section: * before: 0x4c7c * now: 0x4c28 * saved: 84 bytes Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com> |
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apps | ||
core | ||
cpu | ||
dev | ||
doc | ||
examples | ||
platform | ||
regression-tests | ||
tools | ||
.gitignore | ||
.gitmodules | ||
.travis.yml | ||
CONTRIBUTING.md | ||
LICENSE | ||
Makefile.include | ||
README-BUILDING.md | ||
README-EXAMPLES.md | ||
README.md |
The Contiki Operating System
Contiki is an open source operating system that runs on tiny low-power microcontrollers and makes it possible to develop applications that make efficient use of the hardware while providing standardized low-power wireless communication for a range of hardware platforms.
Contiki is used in numerous commercial and non-commercial systems, such as city sound monitoring, street lights, networked electrical power meters, industrial monitoring, radiation monitoring, construction site monitoring, alarm systems, remote house monitoring, and so on.
For more information, see the Contiki website: