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/**
* FILE: main.s
*
* DESCRIPTION:
* An STM32F401, button interrupt driver written entirely in Assembler.
*
* AUTHOR: Kevin Thomas
* CREATION DATE: March 9, 2024
* UPDATE DATE: June 27, 2025
*/
.syntax unified // use unified assembly syntax
.cpu cortex-m4 // target Cortex-M4 core
.fpu softvfp // use software floating point
.thumb // use Thumb instruction set
/**
* The start address for the .data section defined in linker script.
*/
.word _sdata // start of .data
/**
* The end address for the .data section defined in linker script.
*/
.word _edata // end of .data
/**
* The start address for the initialization values of the .data section defined in
* linker script.
*/
.word _sidata // start of .data init values
/**
* The start address for the .bss section defined in linker script.
*/
.word _sbss // start of .bss
/**
* The end address for the .bss section defined in linker script.
*/
.word _ebss // end of .bss
/**
* Provide weak aliases for each Exception handler to the Default_Handler. As they
* are weak aliases, any function with the same name will override this definition.
*/
.macro weak name
.global \name // make symbol global
.weak \name // mark as weak
.thumb_set \name, Default_Handler // set to Default_Handler
.word \name // vector entry
.endm
/**
* Initialize the .isr_vector section. The .isr_vector section contains vector
* table.
*/
.section .isr_vector, "a" // vector table section
/**
* The STM32F401RE vector table. Note that the proper constructs must be placed
* on this to ensure that it ends up at physical address 0x00000000.
*/
.global isr_vector // export vector table
.type isr_vector, %object // object type
isr_vector:
.word _estack // Initial Stack Pointer
.word Reset_Handler // Reset Handler
weak NMI_Handler // NMI Handler
weak HardFault_Handler // HardFault Handler
weak MemManage_Handler // MemManage Handler
weak BusFault_Handler // BusFault Handler
weak UsageFault_Handler // UsageFault Handler
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
weak SVC_Handler // SVC Handler
weak DebugMon_Handler // Debug Monitor Handler
.word 0 // Reserved
weak PendSV_Handler // PendSV Handler
weak SysTick_Handler // SysTick Handler
.word 0 // Reserved
weak EXTI16_PVD_IRQHandler // EXTI Line 16 Interrupt PVD
weak TAMP_STAMP_IRQHandler // Tamper/TimeStamp Interrupt
weak EXTI22_RTC_WKUP_IRQHandler // RTC Wakeup Interrupt
weak FLASH_IRQHandler // FLASH Global Interrupt
weak RCC_IRQHandler // RCC Global Interrupt
weak EXTI0_IRQHandler // EXTI Line0 Interrupt
weak EXTI1_IRQHandler // EXTI Line1 Interrupt
weak EXTI2_IRQHandler // EXTI Line2 Interrupt
weak EXTI3_IRQHandler // EXTI Line3 Interrupt
weak EXTI4_IRQHandler // EXTI Line4 Interrupt
weak DMA1_Stream0_IRQHandler // DMA1 Stream0 Global Interrupt
weak DMA1_Stream1_IRQHandler // DMA1 Stream1 Global Interrupt
weak DMA1_Stream2_IRQHandler // DMA1 Stream2 Global Interrupt
weak DMA1_Stream3_IRQHandler // DMA1 Stream3 Global Interrupt
weak DMA1_Stream4_IRQHandler // DMA1 Stream4 Global Interrupt
weak DMA1_Stream5_IRQHandler // DMA1 Stream5 Global Interrupt
weak DMA1_Stream6_IRQHandler // DMA1 Stream6 Global Interrupt
weak ADC_IRQHandler // ADC1 Global Interrupt
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
weak EXTI9_5_IRQHandler // EXTI Line[9:5] Interrupts
weak TIM1_BRK_TIM9_IRQHandle // TIM1 Break/TIM9 Global Interrupt
weak TIM1_UP_TIM10_IRQHandler // TIM1 Update/TIM10 Global Interrupt
weak TIM1_TRG_COM_TIM11_IRQHandler // TIM1 T/C/TIM11 Global Interrupt
weak TIM1_CC_IRQHandler // TIM1 Capture Compare Interrupt
weak TIM2_IRQHandler // TIM2 Global Interrupt
weak TIM3_IRQHandler // TIM3 Global Interrupt
weak TIM4_IRQHandler // TIM4 Global Interrupt
weak I2C1_EV_IRQHandler // I2C1 Event Interrupt
weak I2C1_ER_IRQHandler // I2C1 Error Interrupt
weak I2C2_EV_IRQHandler // I2C2 Event Interrupt
weak I2C2_ER_IRQHandler // I2C2 Error Interrupt
weak SPI1_IRQHandler // SPI1 Global Interrupt
weak SPI2_IRQHandler // SPI2 Global Interrupt
weak USART1_IRQHandler // USART1 Global Interrupt
weak USART2_IRQHandler // USART2 Global Interrupt
.word 0 // Reserved
weak EXTI15_10_IRQHandler // EXTI Line[15:10] Interrupts
weak EXTI17_RTC_Alarm_IRQHandler // RTC Alarms EXTI
weak EXTI18_OTG_FS_WKUP_IRQHandler // USB OTG FS Wakeup EXTI
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
weak DMA1_Stream7_IRQHandler // DMA1 Stream7 Global Interrupt
.word 0 // Reserved
weak SDIO_IRQHandler // SDIO Global Interrupt
weak TIM5_IRQHandler // TIM5 Global Interrupt
weak SPI3_IRQHandler // SPI3 Global Interrupt
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
weak DMA2_Stream0_IRQHandler // DMA2 Stream0 Global Interrupt
weak DMA2_Stream1_IRQHandler // DMA2 Stream1 Global Interrupt
weak DMA2_Stream2_IRQHandler // DMA2 Stream2 Global Interrupt
weak DMA2_Stream3_IRQHandler // DMA2 Stream3 Global Interrupt
weak DMA2_Stream4_IRQHandler // DMA2 Stream4 Global Interrupt
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
weak OTG_FS_IRQHandler // USB OTG FS Global Interrupt
weak DMA2_Stream5_IRQHandler // DMA2 Stream5 Global Interrupt
weak DMA2_Stream6_IRQHandler // DMA2 Stream6 Global Interrupt
weak DMA2_Stream7_IRQHandler // DMA2 Stream7 Global Interrupt
weak USART6_IRQHandler // USART6 Global Interrupt
weak I2C3_EV_IRQHandler // I2C3 Event Interrupt
weak I2C3_ER_IRQHandler // I2C3 Error Interrupt
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
.word 0 // Reserved
weak SPI4_IRQHandler // SPI4 Global Interrupt
/**
* @brief This code is called when processor starts execution.
*
* @details This is the code that gets called when the processor first
* starts execution following a reset event. We first define and init
* the bss section and then define and init the data section, after which
* the application supplied main routine is called.
*
* @param None
* @retval None
*/
.type Reset_Handler, %function // function type
.global Reset_Handler // export symbol
Reset_Handler:
.Reset_Handler_Setup:
LDR R4, =_estack // load addr at end of stack R4
MOV SP, R4 // move addr at end of stack SP
LDR R4, =_sdata // copy data seg init flash to SRAM
LDR R5, =_edata // copy data seg init flash to SRAM
LDR R6, =_sidata // copy data seg init flash to SRAM
MOVS R7, #0 // zero offset
B .Reset_Handler_Loop_Copy_Data_Init // branch
.Reset_Handler_Copy_Data_Init:
LDR R8, [R6, R7] // copy data seg init to regs
STR R8, [R4, R7] // copy data seg init tp regs
ADDS R7, R7, #4 // increment offset
.Reset_Handler_Loop_Copy_Data_Init:
ADDS R8, R4, R7 // initialize the data segment
CMP R8, R5 // compare
BCC .Reset_Handler_Copy_Data_Init // branch if carry is clear
LDR R6, =_sbss // copy bss seg init flash to SRAM
LDR R8, =_ebss // copy bss seg init flash to SRAM
MOVS R7, #0 // zero offset
B .Reset_Handler_Loop_Fill_Zero_BSS // branch
.Reset_Handler_Fill_Zero_BSS:
STR R7, [R6] // zero fill the bss segment
ADDS R6, R6, #4 // increment pointer
.Reset_Handler_Loop_Fill_Zero_BSS:
CMP R6, R8 // compare
BCC .Reset_Handler_Fill_Zero_BSS // branch if carry is clear
.Reset_Handler_Call_Main:
BL main // call main
/**
* @brief This code is called when the processor receives an unexpected interrupt.
*
* @details This simply enters an infinite loop, preserving the system state for
* examination by a debugger.
*
* @param None
* @retval None
*/
.type Default_Handler, %function // function type
.global Default_Handler // export symbol
Default_Handler:
BKPT // set processor into debug state
B.N Default_Handler // infinite loop
/**
* Initialize the .text section.
* The .text section contains executable code.
*/
.section .text // code section
/**
* @brief Entry point for initialization and setup of specific functions.
*
* This function is the entry point for initializing and setting up specific
* functions. It calls other functions to enable certain features and then
* enters a loop for further execution.
*
* @param None
* @retval None
*/
.type main, %function
.global main
main:
.Push_Registers:
PUSH {R4-R12, LR} // push registers R4-R12, LR to the stack
.GPIOC_Enable:
BL GPIOC_Enable // call function
.GPIOC_PC13_EXTI_Init:
BL GPIOC_PC13_EXTI_Init // call function
.Loop:
BL Loop // call function
.Pop_Registers:
POP {R4-R12, LR} // pop registers R4-R12, LR from the stack
BX LR // return to caller
/**
* @brief Enables the GPIOC peripheral by setting the corresponding RCC_AHB1ENR bit.
*
* @details This function enables the GPIOC peripheral by setting the corresponding RCC_AHB1ENR bit.
* It loads the address of the RCC_AHB1ENR register, retrieves the current value of the
* register, sets the GPIOCEN bit, and stores the updated value back into the register.
*
* @param None
* @retval None
*/
GPIOC_Enable:
.GPIOC_Enable_Push_Registers:
PUSH {R4-R12, LR} // push registers R4-R12, LR to the stack
.GPIOC_Enable_Set_RCC_AHB1ENR:
LDR R4, =0x40023830 // load address of RCC_AHB1ENR register
LDR R5, [R4] // load value inside RCC_AHB1ENR register
ORR R5, #(1<<2) // set the GPIOCEN bit
STR R5, [R4] // store value into RCC_AHB1ENR register
.GPIOC_Enable_Pop_Registers:
POP {R4-R12, LR} // pop registers R4-R12, LR from the stack
BX LR // return to caller
/**
* @brief Initializes GPIOC PC13 for EXTI interrupt.
*
* @details This function configures GPIOC PC13 for EXTI interrupt. It sets the pin's mode
* to input and enables the internal pull-up resistor. Additionally, it enables the
* EXTI interrupt for PC13, configures SYSCFG_EXTICR4, and sets the corresponding
* EXTI and NVIC settings to enable interrupt handling for PC13.
*
* @param None
* @retval None
*/
GPIOC_PC13_EXTI_Init:
.GPIOC_PC13_EXTI_Init_Push_Registers:
PUSH {R4-R12, LR} // push registers R4-R12, LR to the stack
.GPIOC_PC13_EXTI_Init_Disable_Global_Interrupts:
CPSID I // disable global interrupts
.GPIOC_PC13_EXTI_Init_Set_GPIOC_MODER:
LDR R4, =0x40020800 // load address of GPIOC_MODER register
LDR R5, [R1] // load value inside GPIOC_MODER register
AND R5, #~(1<<27) // clear the MODER13 bit
AND R5, #~(1<<26) // clear the MODER13 bit
STR R5, [R4] // store value into GPIOC_MODER register
.GPIOC_PC13_EXTI_Init_Set_GPIOC_PUPDR:
LDR R4, =0x4002080C // load address of GPIOC_PUPDR register
LDR R5, [R4] // load value inside GPIOC_PUPDR register
AND R5, #~(1<<27) // clear the PUPDR13 bit
ORR R5, #(1<<26) // set the PUPDR13 bit
STR R5, [R4] // store value into GPIOC_PUPDR register
.GPIOC_PC13_EXTI_Init_Set_RCC_APB2ENR:
LDR R4, =0x40023844 // load address of RCC_ABP2ENR
LDR R5, [R4] // load value inside RCC_ABP2ENR register
ORR R5, #(1<<14) // set SYSCFGEN bit
STR R5, [R4] // store value into RCC_APB2ENR register
.GPIOC_PC13_EXTI_Init_Set_SYSCFG_EXTICR4:
LDR R4, =0x40013814 // load address of SYSCFG_EXTICR4
LDR R5, [R1] // load value inside SYSCFG_EXTICR4 register
ORR R5, #(1<<5) // set EXTI13 bit
STR R5, [R4] // store value into SYSCFG_EXTICR4 register
.GPIOC_PC13_EXTI_Init_Set_EXTI_IMR:
LDR R4, =0x40013C00 // load address of EXTI_IMR register
LDR R5, [R4] // load value inside EXTI_IMR register
ORR R5, #(1<<13) // set MR13 bit
STR R5, [R4] // store value into EXTI_IMR register
.GPIOC_PC13_EXTI_Init_Set_EXTI_FTSR:
LDR R4, =0x40013C0C // load address of EXTI_FTSR register
LDR R5, [R4] // load value inside EXTI_FTSR register
ORR R5, #(1<<13) // set TR13 bit
STR R5, [R4] // store value into EXTI_IMR register
.GPIOC_PC13_EXTI_Init_Enable_NVIC_IRQ:
BL NVIC_EnableIRQ_EXTI15_10 // call function
.GPIOC_PC13_EXTI_Init_Enable_Global_Interrupts:
CPSIE I // enable global interrupts
.GPIOC_PC13_EXTI_Init_Pop_Registers:
POP {R4-R12, LR} // pop registers R4-R12, LR from the stack
BX LR // return to caller
/**
* @brief EXTI callback function for button control.
*
* @details This EXTI callback function handles a button press on the main board
* of the MCU.
*
* @param None
* @retval None
*/
EXTI_Callback:
.EXTI_Callback_Push_Registers:
PUSH {R4-R12, LR} // push registers R4-R12, LR to the stack
.EXTI_Callback_NOP:
NOP // no op to be a placeholder for practical func
.EXTI_Callback_Pop_Registers:
POP {R4-R12, LR} // pop registers R4-R12, LR from the stack
BX LR // return to caller
/**
* @brief Enable NVIC (Nested Vectored Interrupt Controller) for EXTI15_10 interrupts.
*
* @details This function enables the NVIC for EXTI15_10 interrupts. It specifically targets
* the NVIC_ISER1 register, which controls interrupts 32 to 63, and sets the bit
* corresponding to EXTI15_10 (bit 8) to enable the interrupt handling for EXTI lines
* 15 to 10.
*
* @param None
* @retval None
*/
NVIC_EnableIRQ_EXTI15_10:
.NVIC_EnableIRQ_EXTI15_10_Push_Registers:
PUSH {R4-R12, LR} // push registers R4-R12, LR to the stack
.NVIC_EnableIRQ_EXTI15_10_Set_NVIC_ISER1:
LDR R4, =0xE000E104 // NVIC_ISER1, p 683 M7 Arch ref manual, ISER1 interrupts 32-63
LDR R5, [R4] // load value inside NVIC_ISER1 register
ORR R5, #(1<<8) // EXTI15_10 (p 204 Ref Manual), p 210 M4 PM, ISER1 8 = EXTI15_10
STR R5, [R4] // store value into R0
.NVIC_EnableIRQ_EXTI15_10_Pop_Registers:
POP {R4-R12, LR} // pop registers R4-R12, LR from the stack
BX LR // return to caller
/**
* @brief Infinite loop function.
*
* @details This function implements an infinite loop using an unconditional branch
* (B) statement. It is designed to keep the program running indefinitely
* by branching back to itself.
*
* @param None
* @retval None
*/
Loop:
B . // branch infinite loop
/**
* Test data and constants.
* The .rodata section is used for constants and static data.
*/
.section .rodata // read-only data section
/**
* Initialized global data.
* The .data section is used for initialized global or static variables.
*/
.section .data // data section
/**
* Uninitialized global data.
* The .bss section is used for uninitialized global or static variables.
*/
.section .bss // BSS section