mirror of https://github.com/ARMmbed/mbed-os.git
a0c53896e0
LXT/HXT are external crystl oscillator and can be absent on custom board.
This enables configuring LXT/HXT presence:
1. By default, LXT/HXT are configured to be present, except M252 which has no HXT.
2. When LXT is configured to not present, lp_ticker/watchdog will clock by LIRC instead.
3. Limitations:
(1) On all targets, LIRC-clocked lp_ticker gets inaccurate and fails to pass tests.
(2) On NUC472/M453, HIRC-clocked PLL doesn't output 1MHz-aligned frequency. us_ticker gets slight inaccurate.
(3) On all targets, LIRC-clocked RTC is not supported due to no H/W path/RTC clock source reset to LXT on reset/RTC not trimmed for other clock rates.
4. On M263, TRNG's clock source defaults to LXT and needs special handling without LXT.
5. On M252, replace target.hxt-enable with target.hxt-present for consistency.
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| .. | ||
| Reg | ||
| StdDriver | ||
| TOOLCHAIN_ARMC6 | ||
| TOOLCHAIN_GCC_ARM | ||
| TOOLCHAIN_IAR | ||
| M251.h | ||
| M251_mem.h | ||
| M251_mem.icf.h | ||
| cmsis.h | ||
| cmsis_nvic.h | ||
| startup_M251.c | ||
| system_M251.c | ||
| system_M251.h | ||