; ARM assembly tutorial for Asmonite, example 18 for the Blue Pill (STM32F103, Arm Cortex-M3). ; Adapted from the ARM-ASM-Tutorial by Niklas Guertler (example BlinkSysTickInterrupt); see ..\LICENSE.txt. ; ; The SysTick interrupt example on the chip of the original tutorial. The SysTick, the vector table, VTOR and ; the IT blocks are the same as on the Pico 2 (the Cortex-M3 and the Cortex-M33 share them); only the LED is ; switched the way of the STM32: GPIOC_BSRR, bit 29 clears PC13 (LED on), bit 13 sets it (LED off). ; The program runs in the RAM; the core runs from the internal 8 MHz oscillator (HSI) after a reset, so an ; event of the SysTick (1500000 cycles) is about 0.19 s. .target stm32f103 .arch thumb .imagebase 0x20000000 RCC_APB2ENR equ 0x40021018 IOPCEN equ 1 << 4 GPIOC_BASE equ 0x40011000 GPIO_CRH equ 0x04 GPIO_BSRR equ 0x10 LED_ON equ 1 << 29 ; BR13: PC13 low LED_OFF equ 1 << 13 ; BS13: PC13 high SCS_BASE equ 0xe000e000 SYST_CSR equ 0x10 SYST_RVR equ 0x14 SYST_CVR equ 0x18 SCB_VTOR equ 0xd08 TIMER_VALUE equ 1500000 SRAM_END equ 0x20005000 vectors: dd SRAM_END ; 0: the stack pointer at the start dd _start + 1 ; 1: reset dd hang + 1 ; 2: NMI dd hang + 1 ; 3: HardFault dd hang + 1 ; 4: MemManage dd hang + 1 ; 5: BusFault dd hang + 1 ; 6: UsageFault dd 0, 0, 0, 0 ; 7 .. 10: reserved dd hang + 1 ; 11: SVCall dd hang + 1 ; 12: DebugMonitor dd 0 ; 13: reserved dd hang + 1 ; 14: PendSV dd systick_handler + 1 ; 15: SysTick _start: ldr r0, lit_scs adr r1, vectors str r1, [r0, #SCB_VTOR] ; the vector table is ours adr r0, blink_step movs r1, #0 strb r1, [r0] ; blink_step = 0 adr r2, blink_table ldrb r1, [r2] adr r0, timer_events strb r1, [r0] ; timer_events = the first entry of the table bl setup_led ldr r0, lit_gpioc ldr r1, lit_led_on str r1, [r0, #GPIO_BSRR] ; the first step: LED on ldr r0, lit_timer_value bl start_systick cpsie i ; allow interrupts (PRIMASK = 0) sleep_loop: wfi ; sleep until an interrupt b sleep_loop ; ---- called by the SysTick at every event ---- systick_handler: adr r0, timer_events ldrb r3, [r0] subs r3, r3, #1 ; one event less itt ne strbne r3, [r0] ; not yet 0: store it bne handler_done ; and return adr r0, blink_step ldrb r1, [r0] adds r1, r1, #1 ; the next entry cmp r1, #(blink_table_end - blink_table) it hs movhs r1, #0 ; after the last one: from the start again strb r1, [r0] adr r2, blink_table ldrb r3, [r2, r1] ; its number of events adr r0, timer_events strb r3, [r0] tst r1, #1 ; even entry: on, odd entry: off ite eq ldreq r2, lit_led_on ldrne r2, lit_led_off ldr r0, lit_gpioc str r2, [r0, #GPIO_BSRR] handler_done: bx lr ; ---- start the SysTick with its interrupt: r0 = cycles between two events ---- start_systick: ldr r1, lit_scs str r0, [r1, #SYST_RVR] movs r0, #0 str r0, [r1, #SYST_CVR] movs r0, #7 ; ENABLE | TICKINT | CLKSOURCE str r0, [r1, #SYST_CSR] bx lr ; ---- the clock of port C on, PC13 an output (push-pull, 2 MHz); changes r0, r1 ---- setup_led: ldr r1, lit_rcc_apb2enr ldr r0, [r1] orr r0, r0, #IOPCEN str r0, [r1] ldr r1, lit_gpioc ldr r0, [r1, #GPIO_CRH] bic r0, r0, #0x00f00000 orr r0, r0, #0x00200000 str r0, [r1, #GPIO_CRH] bx lr hang: b hang blink_table: db 2, 2, 2, 2, 2, 2 db 5, 2, 5, 2, 5, 2 db 2, 2, 2, 2, 2, 8 blink_table_end: blink_step: db 0 timer_events: db 0 align 4 lit_rcc_apb2enr: dd RCC_APB2ENR lit_gpioc: dd GPIOC_BASE lit_led_on: dd LED_ON lit_led_off: dd LED_OFF lit_scs: dd SCS_BASE lit_timer_value: dd TIMER_VALUE