Arduino與LoRa
自從去年Arduino增加了對(duì)于STM32以及Semtech LoRa的支持后袭灯,基于Arduino的開發(fā)得到了長足的發(fā)展往核。由于Arduino不局限于ARM內(nèi)核赁酝,MCU多樣性比較高清焕,至少可以使用ESP8266/ESP32/STM32/AVR/PIC/K20等罕模。而Arduino社交化程度比較高匹中。
在同一硬件中,編程平臺(tái)朱浴、協(xié)議棧吊圾、應(yīng)用的復(fù)雜度呈現(xiàn)幾何級(jí)數(shù)上升。但不管如何翰蠢,選擇受眾多项乒,開發(fā)易的平臺(tái)依然很有用。
SPI 驅(qū)動(dòng)
無論是Arduino/mbed/MicroPython/Lua/JavaScript梁沧,驅(qū)動(dòng)LoRa的接口最簡單:SPI檀何,四線SPI加上RST/D0中斷即可。要調(diào)通SPI總線廷支,必須依賴一個(gè)工具:邏輯分析儀频鉴,淘寶D版。
Fig 1: Arduino firmware, abnormal SPI operation for leading pulse
Arduino的SPI驅(qū)動(dòng)中有個(gè)SPI參數(shù)配置:
SPISettings _spiSettings(8E6, MSBFIRST, SPI_MODE0);
一開始我把它放在CS拉低之后恋拍,發(fā)現(xiàn)其初始化會(huì)導(dǎo)致一個(gè)毛刺垛孔,形成9個(gè)脈沖,導(dǎo)致總線出錯(cuò)施敢。參見附圖1周荐。
Fig2 : Arduino firmware, normal SPI operation for leading pulse outside of CS period
于是我把參數(shù)設(shè)置放置在CS拉低之前。
uint8_t singleTransfer(uint8_t address, uint8_t value)
{
uint8_t response;
_spiSettings = SPISettings(FREQ, MSBFIRST, SPI_MODE0);
SPI.beginTransaction(_spiSettings);
digitalWrite(SS, LOW);
SPI.transfer(address);
response = SPI.transfer(value);
SPI.endTransaction();
digitalWrite(SS, HIGH);
return response;
}
這段代碼中悯姊,先初始化配置羡藐,然后拉低CS,然后進(jìn)行傳輸悯许,最后要關(guān)閉SPI仆嗦。參見附圖,即便有個(gè)毛刺先壕,也是在CS周期之外瘩扼。所以總線讀寫正常。但是返回二進(jìn)制卻總是0xFF或0x00垃僚。
Fig3: mbed firmware, normal SPI operation
由于mbed/Arduino共享目標(biāo)板和STLINK集绰,我立刻下載了一個(gè)mbed固件,發(fā)現(xiàn)mbed的確總線比較干凈谆棺,返回值也正確:0x12栽燕,是SX127X的返回值罕袋。參考附圖3。
Fig4: Arduino firmware, normal SPI operation
由于SPI總線硬件無需驗(yàn)證碍岔,剩下的就是總線速率和RST引腳浴讯,所以將總線速度升到8MHz,POR之后RST對(duì)SX127X拉低20ms后拉高“玻現(xiàn)在Arduino的代碼也可以返回0x12了榆纽。但是CS的周期很長,比較怪異捏肢。
ESP8266/STM32
ESP8266的驅(qū)動(dòng)略有不同奈籽。接下來,我會(huì)將常見的LoRa PHY驅(qū)動(dòng)集成在SPI之上鸵赫。Arduino好像不支持printf()衣屏,需要打碎成為多個(gè)print()函數(shù)。略有不便辩棒。
代碼
#include <SPI.h>
#define LED_BP PC13 // BluePill
#define REG_VERSION 0x42
#define RST A0 //PA0 //2
#define SS D10 //PB6 //15
#define FREQ 8E6
SPISettings _spiSettings(8E6, MSBFIRST, SPI_MODE0);
uint8_t singleTransfer(uint8_t address, uint8_t value)
{
uint8_t response;
_spiSettings = SPISettings(FREQ, MSBFIRST, SPI_MODE0);
SPI.beginTransaction(_spiSettings);
digitalWrite(SS, LOW);
SPI.transfer(address);
response = SPI.transfer(value);
SPI.endTransaction();
digitalWrite(SS, HIGH);
return response;
}
uint8_t readRegister(uint8_t address)
{
return singleTransfer(address & 0x7f, 0x00);
}
void setup() {
pinMode(LED_BP, OUTPUT);
pinMode(SS,OUTPUT);
pinMode(RST,OUTPUT);
digitalWrite(RST, LOW);
delay(20);
digitalWrite(RST, HIGH);
SPI.begin();
//_spiSettings = SPISettings(1E6, MSBFIRST, SPI_MODE0);
//SPI.beginTransaction(_spiSettings);
Serial.begin(115200);
Serial.println("SPI Test");
}
void loop() {
uint8_t res;
res = readRegister(0x42);
//Serial.printf("Register[0x42] = 0x%02X\n\r",res);
Serial.print("Register[0x42]=0x");
Serial.println(res, HEX);
if (res!=0x12){
digitalWrite(LED_BP, HIGH); // turn the LED on (HIGH is the voltage level)
delay(500); // wait for a second
digitalWrite(LED_BP, LOW); // turn the LED off by making the voltage LOW
delay(500); // wait for a second
}
}