85 lines
2.2 KiB
Markdown
85 lines
2.2 KiB
Markdown
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# dwt_delay
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Microseconds delay lib based on DWT for STM32 or whatever ARM supporting it.
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Just include `dwt_delay.h` in your project, call `DWT_Init()` and then use delays as needed.
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Depending on MCU used, you may need to include another header file (with MCU peripherals defines) in `dwt_delay.h`.
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The `stm32f1xx.h` is included by default, allowing STM32F1xx to start out of the box.
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If you don't use STM32 MCU or CubeMX, read a section at the end.
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Functions are named as DWT_* to be HAL-alike. Feel free to do whatever you like with this lib,
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change names, indents, coding style, use it in LHC firmware.
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## Example
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```c
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/* main.c */
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#include "dwt_delay.h"
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void main (void)
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{
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// Init section of your code
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DWT_Init();
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while(1) {
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// Delay for 42us
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DWT_Delay(42);
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}
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}
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```
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## Notes on Cortex-M0/0+/1
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Unfortunately, these are not supported, since cores have no access to DWT. CMSIS library states:
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```
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Cortex-M0/0+/1 Core Debug Registers are only accessible over DAP and not via processor
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```
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You may want a delay function based on hardware timer instead.
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## What about Cortex-M35/55/85?
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I don't have any of these to check, but in theory they are supported.
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Anyway you have to change `CoreDebug` to `DCB`, because `CoreDebug` is deprecated in these cores.
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Hence, init sequence should be something like:
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```c
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DCB->DEMCR |= DCB_DEMCR_TRCENA_Msk;
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```
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## I'm not with STM but need microsec delays
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There's an option to try! Also suits those, who use STM32, but dont use HAL/LL libs.
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Include a CMSIS header file according to your core in `dwt_delay.c` and change `SystemCoreClock`
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variable to whatever you probably have in the project representing clock frequency (in Hz).
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Something like this:
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```c
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// In dwt_delay.c
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#include "dwt_delay.h"
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#include "core_cm4.h" // CMSIS header
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#define SystemCoreClock NameOfTheGlobalVariableInYourProject_or_AnotherDefine
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// or at least
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#define SystemCoreClock 48000000UL // Clock is 48Mhz
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...
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```
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## Changelog
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- **2018-01-06**
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This lib emerged.
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- **2019-02-19**
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Overflow check added.
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- **2019-03-26**
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Typo in definition fixed. Got back to short and simpler function.
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- **2023-11-21**
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Now it is MIT License. Added warning for Cortex-M0/0+/1 and notes regarding other Cortex-M cores.
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