Difference between revisions of "How to activate HSI and CSI oscillators calibration"
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Contents
1 Article purpose[edit]
The purpose of this article is to explain how to calibrate the HSI and CSI oscillators in the RCC, by using the TIM internal peripheral TIM12 and/or TIM15 assigned to the secure monitor (TF-A or OP-TEE).
These clocks are internal oscillators whose frequency can be affected by temperature and voltage variations. To achieve a good clock accuracy, it is important to provide a mechanism to compensate the effects of these variations.
The clock calibration algorithm is based on the comparison of a timer (fed by HSI or CSI) and a clock is derived from the HSE clock that is considered as always accurate.
TIM12 input 1 is connected to hsi_cal_ck
TIM12 input 2 is connected to csi_cal_ck
TIM15 input 7 is connected to hsi_cal_ck
TIM15 input 8 is connected to csi_cal_ck
Refer to STM32MP15 reference manuals for detailed information on the timers.
The algorithm is implemented in the secure monitor. It compares both clocks and programs a correction factor in the RCC peripheral. There are various ways to trigger this service:
- periodically by the secure monitor itself
- upon kernel request through a dedicated SMC
- upon Arm® Cortex®-M4 request through a SEV
2 How to activate the calibration[edit]
This is done in the secure monitor device tree, in the stm32mp157c-<board>.dts file.
2.1 Configuring the timers[edit]
The timers used for calibration must be dedicated in the secure context. It cannot be used at the same time by the non-secure world.
Example: timer12-input1 is used for HSI and timer12-input2 for CSI
&timers12 {
secure-status = "okay";
st,hsi-cal-input = <1>;
st,csi_cal-input = <2>;
};
&timers15 {
secure-status = "disabled";
st,hsi-cal-input = <7>;
st,csi_cal-input = <8>;
};
2.2 Enabling and configuring the calibration service[edit]
This can be done by enabling options inside the clock device tree section
<noinclude> {{ArticleMainWriter | OlivierB}} {{ReviewersList | GeraldB, OlivierB, LionelD, FabriceG}} {{ArticleApprovedVersion | OlivierB | LoicP | No previous approved version | AnneJ - 4Feb'19 - 10487 | 8Feb'19}} [[Category:How to run use cases]]</noinclude> ==Article purpose== The purpose of this article is to explain how to calibrate the HSI and CSI oscillators in the [[RCC internal peripheral|RCC]], by using the [[TIM_internal_peripheral#Overview|TIM internal peripheral]] '''TIM12''' and/or '''TIM15''' assigned to the secure monitor ([[TF-A overview|TF-A]] or [[OP-TEE overview|OP-TEE]]). These clocks are internal oscillators whose frequency can be affected by temperature and voltage variations. To achieve a good clock accuracy, it is important to provide a mechanism to compensate the effects of these variations. The clock calibration algorithm is based on the comparison of a timer (fed by HSI or CSI) and a clock is derived from the HSE clock that is considered as always accurate. TIM12 input 1 is connected to hsi_cal_ck TIM12 input 2 is connected to csi_cal_ck TIM15 input 7 is connected to hsi_cal_ck TIM15 input 8 is connected to csi_cal_ck Refer to [[STM32MP15 resources#Reference manuals|STM32MP15 reference manuals]] for detailed information on the timers. The algorithm is implemented in the secure monitor. It compares both clocks and programs a correction factor in the RCC peripheral. There are various ways to trigger this service: - periodically by the secure monitor itself - upon kernel request through a dedicated SMC - upon Arm<sup>®</sup> Cortex<sup>®</sup>-M4 request through a SEV ==How to activate the calibration== This is done in the secure monitor device tree, in the stm32mp157c-<board>.dts file. ===Configuring the timers=== The timers used for calibration must be dedicated in the secure context. It cannot be used at the same time by the non-secure world. Example: timer12-input1 is used for HSI and timer12-input2 for CSI &timers12 { secure-status = "okay"; st,hsi-cal-input = <1>; st,csi_cal-input = <2>; }; &timers15 { secure-status = "disabled"; st,hsi-cal-input = <7>; st,csi_cal-input = <8>; }; ===Enabling and configuring the calibration service=== This can be done by enabling options inside the [[Clock_device_tree_configuration_-_Bootloader_specific#HSI_and_CSI_clockclocks_calibration|clock device tree section]] <noinclude> {{PublicationRequestId | 10487 | 2019-02-04 | AnneJ}} [[Category:How to run use cases]]</noinclude>
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==Article purpose== |
==Article purpose== |
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The purpose of this article is to explain how to calibrate the HSI and CSI oscillators in the [[RCC internal peripheral|RCC]], by using the [[TIM_internal_peripheral#Overview|TIM internal peripheral]] '''TIM12''' and/or '''TIM15''' assigned to the secure monitor ([[TF-A overview|TF-A]] or [[OP-TEE overview|OP-TEE]]). |
The purpose of this article is to explain how to calibrate the HSI and CSI oscillators in the [[RCC internal peripheral|RCC]], by using the [[TIM_internal_peripheral#Overview|TIM internal peripheral]] '''TIM12''' and/or '''TIM15''' assigned to the secure monitor ([[TF-A overview|TF-A]] or [[OP-TEE overview|OP-TEE]]). |
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===Enabling and configuring the calibration service=== |
===Enabling and configuring the calibration service=== |
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| − | This can be done by enabling options inside the [[Clock_device_tree_configuration_-_Bootloader_specific# |
+ | This can be done by enabling options inside the [[Clock_device_tree_configuration_-_Bootloader_specific#HSI_and_CSI_clocks_calibration|clock device tree section]] |
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| + | <noinclude> |
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| + | {{PublicationRequestId | 10487 | 2019-02-04 | AnneJ}} |
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| + | [[Category:How to run use cases]] |
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| + | </noinclude> |
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