stm32f401re nucleo: USART programming

[life758]

Posted on November 16, 2015 at 11:38

Hello everybody,

I'm new on the forum and on ST microcontrollers.I'm trying to program the USART in assembly, but I have some issue to write on DR.What am I missing? Somebody can help me, please?*********************************************        SECTION MYDATA:CONST        DATATDR     DCB     ''HELLO WORLD!\r''; statup code....ldr     r0, =0x40023800         ; RCC                ldr     r1, [r0, #0x10]         ; RCC_AHB1RSTR        bic     r1, r1, #1        str     r1, [r0, #0x10]                ldr     r1, [r0, #0x30]         ; RCC_AHB1ENR        orr     r1, r1, #1        str     r1, [r0, #0x30]                ldr     r1, [r0, #0x24]         ; RCC_APB2RSTR        bic     r1, r1, #(1 << 4)        str     r1, [r0, #0x24]                ldr     r1, [r0, #0x44]         ; RCC_APB2ENR        orr     r1, r1, #(1 << 4)        str     r1, [r0, #0x44]                ldr     r0, =0x40020000         ; Configurazione della GPIOA                ldr     r1, [r0]                ; GPIOA_MODER        bic     r1, r1, #(15 << 2*9)    ; Mask PA9/10        orr     r1, r1, #(10 << 2*9)    ; =AF mode        str     r1, [r0]                ldr     r1, [r0, #0x4]          ; GPIOA_OTYPER        bic     r1, r1, #(3 << 9)       ; Mask PA9/10, 0= push pull        str     r1, [r0, #0x4]                ldr     r1, [r0, #0x8]          ; GPIOA_OSPEEDR        bic     r1, r1, #(15 << 2*9)    ; Mask PA9/10        orr     r1, r1, #(10 << 2*9)    ; =fast speed        str     r1, [r0, #0x8]                ldr     r1, [r0, #0xC]          ; GPIOA_PUPDR        bic     r1, r1, #(15 << 2*9)    ; Mask PA9/10. =no pull        ;orr     r1, r1, #(5 << 2*9)    ; =pull-up        str     r1, [r0, #0xC]                ldr     r1, [r0, #0x24]         ; GPIOA_AFRH        bic     r1, r1, #(0xFF << 4*1)  ; Mask PA9/10        orr     r1, r1, #(0x77 << 4*1)  ; =AF7, USART1        str     r1, [r0, #0x24]                        ; Init_USART1                                        ;                                        ;        ldr     r0, =0x40011000         ; USART1                ldr     r1, =0xC00080           ; =reset value        str     r1, [r0]                ; SR                ldr     r1, =0x683              ; =USARTDIV. per ottenere 9600bps a partire da HSI        str     r1, [r0, #0x8]          ; BRR                ldr     r1, =0                  ; =reset value        str     r1, [r0, #0x10]         ; CR2. 1 stop bit                ldr     r1, =0x8        str     r1, [r0, #0x14]         ; CR3. =half-duplex selected                ldr     r1, =0        str     r1, [r0, #0x18]         ; GTPR. =reset value                        ldr     r1, =0x2088             ; CR1. over=16, data bits=8, TE=1, TXEIE=1        str     r1, [r0, #0xC]                            B       main                        SECTION .text:CODE:NOROOT(2)        THUMB        main    NOP        LDR     r2, =TDR                ; carico in r2 l'indirizzo della base                                        ; di memoria in cui è memorizzata la                                        ; stringa ''HELLO WORLD!''polling        ldr     r1, [r0]                ; USART1_SR        ands    r1, r1, #(1 << 7)       ; se TXE=0 rimane nel polling        beq     polling        ldrb    r3, [r2], #1            ; carica il valore puntato da r2 e poi r2++ (byte)        cmp     r3, #'\r'        beq     main                    ; se sono uguali salta l'istruzione di memorizzare in USART1_DR        ldr     r4, [r0]        strh    r3, [r0, #0x4]          ; scrive il dato da trasmettere nello USART1_DR        B       polling*********************************************ps: I'm modify the startup code given by STpps: I'm using IAR to write my program

[Tesla DeLorean]

Posted on November 16, 2015 at 15:01

but I have some issue to write on DR

What does that actually mean? What issue? Your comments suggest you enable an interrupt, why would you do that, you have no handler, or NVIC configuration. The Nucleo's VCP port is USART2 PA2/PA3

[life758]

Posted on November 16, 2015 at 16:12

My final goal is to use the USART to modify the duty cycle of a PWM waveform generated from a timer. In the final project I want to use the interrupts, so I leave the option for later on, but I know that option don't make any difference, because I need to configure the NVIC first.

Anyway my issue was in debugging mode, where I couldn't see the output on DR and the reset of TXE by hardware. After I wrote the post I decided to observe the output on PA9 with the oscilloscope and I was glad to see the USART working. I was stupid and a little bit lazy. Sorry!At the moment I'm trying to send data form PC and receive the same data from nucleosorry for my poor english

[Tesla DeLorean]

Posted on November 16, 2015 at 17:16

Unhandled interrupts can result in the Cortex-Mx getting stuck trying to handle something that is never cleared, ie it never leaves interrupt state, and foreground code stops executing.

[Tesla DeLorean]

Posted on November 16, 2015 at 17:18

Peripheral register are not RAM, you often can't view the content written into logic structures that consume the data internally. In many cases the read and write view different registers.

[life758]

Posted on November 16, 2015 at 19:05

Thanks Mr. Clive!

I appreciate your patience and kindness!I choose to leave TXEIE=1 to understand how interrupts works and seems if I don't configure the NVIC it doesn't matter if TXEIE=1 or =0next step. use interrupts to transmit/receive data from/to pc

[life758]

Posted on November 18, 2015 at 10:27

Hello everybody!

I wrote the code to send data from PC to nucleo and get back the same data from nucleo. I used as interrupt the RxNE flag.The code works ok and I would to ask you if I can improve my code to make it faster and more reliable.;***************************************************;;; Subroutines-----------------------------------------------------------------        section get:CODE:NOROOT(2)get_char        add     r8, r8, #1        ldrb    r3, [r0, #4]            ; get char on r3                BX      LR                      ; return from function call                        section put:CODE:NOROOT(2)put_char        ldr     r1, [r0]                ; SR        ands    r1, r1, #(1 << 7)        beq     put_char                ; polling on TXE        add     r9, r9, #1        strb    r3, [r0, #4] ; transmit the data received on r3        BX      LR;;; End Subroutines-------------------------------------------------------------                SECTION .text:CODE:NOROOT(2)        THUMB        main    NOP        WFI ; MCU in sleep mode until RXNE=1        B       main;;; Interrupts definition------------------------------------------------PUBLIC USART1_IRQ37        SECTION .text:CODE:REORDER:NOROOT(1)USART1_IRQ37        push    {LR}        BL      get_char                        BL      put_char        pop     {LR}        BX      LR;*****************************************regards