问题描述
我在尝试将 LED 连接到树莓派上的 gpio 引脚 18 时遇到问题.我已经用 C 测试了我的设置并确认这不是问题，但我的汇编代码是问题.
I have a problem trying to get an LED connected to gpio pin 18 on the raspberry pi. I have tested my setup with C and have confirmed thats not the problem, but my assembly code is the problem.
这是我目前的代码:
.global main
main:
SUB SP, SP, #16 @ Create 16 bytes storage
LDR R0, .addr_file @ get GPIO Controller addr
LDR R1, .flags @ set flag permissions
BL open @ call to get file handle
STR R0, [SP, #12] @ File handle number
LDR R3, [SP, #12] @ Get File handle
STR R3, [SP, #0] @ Store file handle on top stack
LDR R3, .gpiobase @ get GPIO_Base address
STR R3, [SP, #4] @ store on SP+4
MOV R0, #0 @ R0=0
MOV R1, #4096 @ R1=page
MOV R2, #3 @ R2=3
MOV R3, #1 @ R3=1 (stdouts)
BL mmap @ call libc fct for mmap
STR R0, [SP, #16] @ store virtual mem addr
LDR R3, [SP, #16] @ get virtual mem addr
fctsel:
ADD R3, R3, #4 @ add 4 for block 1 (GPFSEL1)
LDR R2, [SP, #16] @ get virtual mem addr
ADD R2, R2, #16 @ add 4 for block 1 (GPFSEL1)
LDR R2, [R2, #0] @ load R2 with value at R2
BIC R2, R2, #0b111<<24 @ Bitwise clear of three bits
STR R2, [R3, #0] @ Store result in Register [set input]
LDR R3, [SP, #16] @ Get virtual mem address
ADD R3, R3, #4 @ Add 4 for block 1 (GPFSEL1)
LDR R2, [SP, #16] @ Get virtual mem addr
ADD R2, R2, #4 @ add 4 for block 1 (GPFSEL1)
LDR R2, [R2, #0] @ Load R2 with value at R2
ORR R2, R2, #1<<24 @ Set bit....
STR R2, [R3, #0] @ ...and make output
on:
LDR R3, [SP, #16] @ get virt mem addr
MOV R4, #1 @ get 1
MOV R2, R4, LSL#18 @ Shift by pin number
STR R2, [R3, #0] @ write to memory
LDR R0, [SP, #12] @ get file handle
BL close @ close file
ADD SP, SP, #16 @ restore SP
MOV R7, #1
SWI 0
.addr_file: .word .file
.flags: .word 1576962
@.gpiobase: .word 0x20200000 @ GPIO_Base for Pi 1
.gpiobase: .word 0x3F200000 @ GPIO_Base for Pi 2
.data
.file: .ascii "/dev/mem\000"
我设法让它与 GPIO 47 引脚一起工作.但是，当我将其更改为使用 pin 18 时，这就是我遇到问题的地方.在此先感谢您的帮助，非常感谢！
I managed to get it working with the GPIO 47 pin. However when I changed it to work with pin 18 this is where I ran into issues. Thanks in advance for any help, its greatly appreciated!
推荐答案
查看 BCM2835 文档 - Broadcom BCM2835 ARM Peripherals https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
Looking at BCM2835 documentation - Broadcom BCM2835 ARM Peripherals https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
您的代码似乎基于 Raspberry Pi、汇编语言、Bruce Smith.
Is seems that your code is based on Raspberry Pi, Assembly Language, Bruce Smith.
我不明白为什么我们要清除 3 位，因为文档说是设置输入.
I'm not why we are clearing the 3 bits since the docs say is sets for input.
*** 我确认它可以在我的 RPi 2 B 上工作，引脚电压为 3+ 伏.
*** I confirmed that it works on my RPi 2 B with 3+ volts on the pin.
目标引脚 = 18设置 GPIO 功能:26-24 FSEL18 FSEL18 - 功能选择 18 R/W 0哪个在 GPIO 替代功能选择寄存器 1 中所以:0x 7E20 0004 GPFSEL1 GPIO 功能选择 1 32 R/W |偏移量#0x4
Target pin = 18Set GPIO Func:26-24 FSEL18 FSEL18 - Function Select 18 R/W 0Which is in GPIO Alternate function select register 1So: 0x 7E20 0004 GPFSEL1 GPIO Function Select 1 32 R/W | offset #0x4
init_output: // init for OUTPUT
ldr r3, [sp, #8] // virt GPIO base
add r3, r3, #0x4 // offset to GPFSEL1
ldr r2, [r3] // get contents of GPFSEL1
orr r2, r2, #0b001<<18 // set 3 bits re FSEL18 output
str r2, [r3] // store set bits at GPFSEL1
设置输出:31-0 SETn (n=0..31) 0 = 无效 1 = 设置 GPIO 引脚 n R/W 0这是在 GPIO 输出设置寄存器 0所以:0x 7E20 001C GPSET0 GPIO 引脚输出设置 0 32 W |偏移量#0x1C == 28
Set Output:31-0 SETn (n=0..31) 0 = No effect 1 = Set GPIO pin n R/W 0Which is in GPIO Output Set Register 0So: 0x 7E20 001C GPSET0 GPIO Pin Output Set 0 32 W | offset #0x1C == 28
set_pin:
ldr r3, [sp, #8] // virt GPIO base
add r3, r3, #0x1C // GPSET0
ldr r2, [r3] // get content of GPSET0
orr r2, r2, #1<<18 // set PIN 18
str r2,[r3] // set PIN 18 @ GPSET0
清除输出:31-0 CLRn (n=0..31) 0 = 无效 1 = 清除 GPIO 引脚 n R/W 0哪个是GPIO输出清除寄存器0所以:0x 7E20 0028 GPCLR0 GPIO 引脚输出清除 0 32 W |偏移量#0x28 == 40
Clear Output:31-0 CLRn (n=0..31) 0 = No effect 1 = Clear GPIO pin n R/W 0Which is GPIO Output Clear Register 0So: 0x 7E20 0028 GPCLR0 GPIO Pin Output Clear 0 32 W | offset #0x28 == 40
clear_pin:
ldr r3, [sp, #8] // virt GPIO base
add r3, r3, #0x28 // GPCLR0
ldr r2, [r3] // get content of GPCLR0
orr r2, r2, #1<<18 // set PIN 18
str r2,[r3] // set PIN 18 @ GPCLR0
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