mirror of https://github.com/ARMmbed/mbed-os.git
904d4e4d2b
Runtime code that analysed clock frequency to determine numerator and denominator for conversion to standard 1MHz failed to handle the case of either being 1 correctly. Although it would spot other values that could be performed as shifts, it failed to spot that 1 is "shift by 0", so would end up doing runtime multiply and/or divide by 1. The runtime divide by 1 could be slow on a Cortex-M0 device, increasing interrupt latency. UART character loss on STM32F0 devices has been traced to this incorrect code. Correct the `exact_log2` routine so that `exact_log2(1)` returns 0 to fix this. Original code had a single special no-multiply-or-divide case for hardware clock frequency being exactly 1MHz, as USTICKER is on STM32F0 - this code lacks that but has a more general special case that covers all shift-convertible frequencies like 500kHz or 8MHz, which should be similar speed as shifts are cheap. |
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| TARGET_FLASH_CMSIS_ALGO | ||
| docs | ||
| include/hal | ||
| source | ||
| tests | ||
| usb | ||
| CMakeLists.txt | ||