LinuxSPI应用编程

设备文件

/dev/spidevx.y
x是SPI总线号&＃xff0c;即一组SCLK、MOSI、MISO
y是SPI设备号&＃xff0c;同一条总线上用不同的片选信号区分&＃xff1a;CE0、CE1等
对于树莓派&＃xff0c;启用SPI功能后&＃xff0c;有一条总线&＃xff0c;两个设备&＃xff1a;
/dev/spidev0.0
/dev/spidev0.1
树莓派上还可以通过dtoverlay使能第二条SPI总线&＃xff0c;支持三个设备&＃xff1a;
在config.txt中加入
dtoverlay&＃61;spi1-3cs
树莓派SPI相关PIN定义参考https://pinout.xyz/pinout/spi#

用户空间设备操作ioctl

相关头文件

#include #include #include #include #include


SPI设置&＃xff1a;

1. 时钟电平&＃xff08;CPOL&＃xff09;和采用阶段&＃xff08;CPHA&＃xff09;
2. 时钟频率
3. 片选电平
4. 是否有片选信号
5. 数据位数&＃xff08;通常为8bit&＃xff09;
6. 数据位传输顺序&＃xff08;MSB或LSB&＃xff09;
7. 3线或4线

如果CPOL&＃61;0&＃xff0c;串行同步时钟的空闲状态为低电平&＃xff1b;
如果CPOL&＃61;1&＃xff0c;串行同步时钟的空闲状态为高电平&＃xff1b;
时钟相位(CPHA)能够配置用于选择两种不同的传输协议之一进行数据传输。
如果CPHA&＃61;0&＃xff0c;在串行同步时钟的第一个跳变沿(上升或下降)数据被采样&＃xff1b;
如果CPHA&＃61;1&＃xff0c;在串行同步时钟的第二个跳变沿(上升或下降)数据被采样&＃xff1b;

工作模式由位组合而成&＃xff1a;
SPI_CPHA
SPI_CPOL
SPI_CS_HIGH
SPI_LSB_FIRST
SPI_3WIRE
SPI_NO_CS
更多内容参考spidev.h

数据传输

可以调用read/write进行读写&＃xff0c;也可以使用ioctl同时写并且读。
无论使用哪种方式&＃xff0c;一次读写的最大字节数不能超过spi底层bufsiz&＃xff0c;bufsiz是SPI驱动内核模块参数&＃xff08;TODO 如何修改此参数&＃xff1f;&＃xff1f;&＃xff1f;&＃xff09;
使用ioctl方式可以一次读写多块数据&＃xff0c;多块数据通过spi_ioc_transfer结构数组传递

ioctl参数说明&＃xff1a;

• cmd SPI_IOC_MESSAGE(N) 其中N是spi_ioc_transfer结构数组元素个数
• arg 是spi_ioc_transfer结构数组地址

注意&＃xff1a;每个数据发送和接收的数据长度是相同的&＃xff0c;可以通过将tx_buf置NULL只读或将rx_buf置NULL只写
delay_usecs,speed_hz,bits_per_word等参数可以设置为0&＃xff0c;使用全局或默认设置

由于有发送长度和接收长度一致的限制&＃xff0c;并且通常先发送命令再接收应答而不会同时进行&＃xff0c;所以一般使用read/write就可以了。确实需要同时收发的可以使用两个spi_ioc_transfer结构&＃xff0c;一发一收。

应用举例

以树莓派操作PN532 NFC模块为例&＃xff1a;
PN532采用微雪的PN532 NFC HAT模块&＃xff0c;这个模块有个问题是40PIN的PI接口里片选信号没有接到PI的CE0或CE1&＃xff0c;而是接到了GPIO4&＃xff0c;所以&＃xff0c;我们使用模块上的树莓派插针通过杜邦线与树莓派进行连接&＃xff0c;将D4&＃xff08;GPIO4&＃xff09;接到树莓派的CE0&＃xff0c;其他插针依次对应连接即可。
注意&＃xff1a;电源需要使用模块上的树莓派5V插针连接&＃xff0c;如需使用3.3V&＃xff0c;可以将电源连接到模块控制接口的3.3V和GND。

使用HAT方式连接&＃xff1a;
模块在SPI通信模式下可以使用控制接口的RX作为片选输入&＃xff0c;将模块上的控制接口RX与模块上的树莓派插针CE0或CE1短接&＃xff0c;将拨码开关的NSS设置为OFF&＃xff0c;断开GPIO4与PN532的连接&＃xff0c;这样GPIO4还可以做其他用途。

从树莓派的PIN脚定义上看&＃xff0c;树莓派并没有接收IRQ&＃xff0c;也没有发送H_REQ

PN532的通信参数&＃xff1a;
* The PN532 is configured as slave and is able to communicate with a host controller with a clock (SCK) up to 5MHz.

以下程序读取NFC tag的UID&＃xff1a;

使用libnfc

// To compile this simple example:
// $ gcc -o quick_start_example1 quick_start_example1.c -lnfc
#include
#include
static void
print_hex(const uint8_t *pbtData, const size_t szBytes)
{size_t szPos;for (szPos &＃61; 0; szPos }
int
main(int argc, const char *argv[])
{nfc_device *pnd;nfc_target nt;// Allocate only a pointer to nfc_contextnfc_context *context;// Initialize libnfc and set the nfc_contextnfc_init(&context);if (context &＃61;&＃61; NULL) {printf("Unable to init libnfc (malloc)\n");exit(EXIT_FAILURE);}// Display libnfc versionconst char *acLibnfcVersion &＃61; nfc_version();(void)argc;printf("%s uses libnfc %s\n", argv[0], acLibnfcVersion);// Open, using the first available NFC device which can be in order of selection:// - default device specified using environment variable or// - first specified device in libnfc.conf (/etc/nfc) or// - first specified device in device-configuration directory (/etc/nfc/devices.d) or// - first auto-detected (if feature is not disabled in libnfc.conf) devicepnd &＃61; nfc_open(context, NULL);if (pnd &＃61;&＃61; NULL) {printf("ERROR: %s\n", "Unable to open NFC device.");exit(EXIT_FAILURE);}// Set opened NFC device to initiator modeif (nfc_initiator_init(pnd) <0) {nfc_perror(pnd, "nfc_initiator_init");exit(EXIT_FAILURE);}printf("NFC reader: %s opened\n", nfc_device_get_name(pnd));// Poll for a ISO14443A (MIFARE) tagconst nfc_modulation nmMifare &＃61; {.nmt &＃61; NMT_ISO14443A,.nbr &＃61; NBR_106,};if (nfc_initiator_select_passive_target(pnd, nmMifare, NULL, 0, &nt) > 0) {printf("The following (NFC) ISO14443A tag was found:\n");printf(" ATQA (SENS_RES): ");print_hex(nt.nti.nai.abtAtqa, 2);printf(" UID (NFCID%c): ", (nt.nti.nai.abtUid[0] &＃61;&＃61; 0x08 ? &＃39;3&＃39; : &＃39;1&＃39;));print_hex(nt.nti.nai.abtUid, nt.nti.nai.szUidLen);printf(" SAK (SEL_RES): ");print_hex(&nt.nti.nai.btSak, 1);if (nt.nti.nai.szAtsLen) {printf(" ATS (ATR): ");print_hex(nt.nti.nai.abtAts, nt.nti.nai.szAtsLen);}}// Close NFC devicenfc_close(pnd);// Release the contextnfc_exit(context);exit(EXIT_SUCCESS);
}


使用ioctl/read/write
pn532.h

#pragma once#include namespace pn532
{const uint8_t TFI_H2P &＃61; 0xD4;
const uint8_t TFI_P2H &＃61; 0xD5;#pragma pack(1)
struct ni_frame_header
{uint8_t preamble;uint8_t start_code[2];uint8_t len;uint8_t lcs;uint8_t tfi;
};struct frame_tailer
{uint8_t dcs;uint8_t postamble;
};
#pragma pack()const uint8_t ACK_FRAME[6] &＃61; {0x00, 0x00, 0xFF, 0x00, 0xFF, 0x00};
const uint8_t NACK_FRAME[6] &＃61; {0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00};
const uint8_t ERROR_FRAME[8] &＃61; {0x00, 0x00, 0xFF, 0x01, 0xFF, 0x7F, 0x81, 0x00};typedef std::shared_ptr byte_ptr;
typedef byte_ptr data_ptr;
typedef byte_ptr frame_ptr;uint8_t checksum(const uint8_t * data, int data_len);
uint8_t checksum(data_ptr data, int data_len);
bool validate_checksum(const uint8_t * data, int data_len);
bool validate_checksum(data_ptr data, int data_len);
int cal_frame_len(int data_len);
frame_ptr new_frame(int frame_len);
int make_frame(uint8_t* buf, int buf_len, uint8_t tfi, const uint8_t* data, int data_len);
int make_frame(frame_ptr& frame, uint8_t tfi, data_ptr data, int data_len);const uint8_t SPI_DW &＃61; 0x01;
const uint8_t SPI_DR &＃61; 0x03;
const uint8_t SPI_SR &＃61; 0x02;int cal_spi_frame_len(int data_len);
int make_spi_frame(uint8_t* buf, int buflen, uint8_t spi_tfi, uint8_t tfi, const uint8_t* data, int data_len);
int make_spi_frame(frame_ptr& frame, uint8_t spi_tfi, uint8_t tfi, const uint8_t* data, int data_len);
int make_spi_frame(frame_ptr& frame, uint8_t spi_tfi, uint8_t tfi, data_ptr data, int data_len);}


pn532.cpp

#include "pn532.h"
#include namespace pn532
{uint8_t checksum(const uint8_t * data, int data_len)
{assert(data_len >&＃61; 0);uint8_t cs &＃61; 0;const uint8_t* p &＃61; data;for (int i &＃61; 0; i }uint8_t checksum(data_ptr data, int data_len)
{return checksum(data.get(), data_len);
}bool validate_checksum(const uint8_t* data, int data_len)
{assert(data_len >&＃61; 0);uint8_t cs &＃61; 0;const uint8_t* p &＃61; data;for (int i &＃61; 0; i }bool validate_checksum(data_ptr data, int data_len)
{return validate_checksum(data.get(), data_len);
}int cal_frame_len(int data_len)
{assert(data_len >&＃61; 0);return sizeof(ni_frame_header) &＃43; data_len &＃43; sizeof(frame_tailer);
}frame_ptr new_frame(int frame_len)
{assert(frame_len >&＃61; 0);frame_ptr frame(new uint8_t[frame_len]);return frame;
}int make_frame(uint8_t* buf, int buf_len, uint8_t tfi, const uint8_t* data, int data_len)
{assert(data_len >&＃61; 0);int frame_len &＃61; cal_frame_len(data_len);if (buf &＃61;&＃61; NULL || buf_len &＃61;&＃61; 0){return frame_len;}if (buf_len preamble &＃61; 0x00;h->start_code[0] &＃61; 0x00;h->start_code[1] &＃61; 0xFF;h->len &＃61; data_len &＃43; 1;h->lcs &＃61; checksum(&h->len, 1);h->tfi &＃61; tfi;uint8_t dcs &＃61; tfi;const uint8_t* dd &＃61; data;for (int i &＃61; 0; i dcs &＃61; dcs;t->postamble &＃61; 0x00;return frame_len;
}int make_frame(frame_ptr & frame, uint8_t tfi, data_ptr data, int data_len)
{assert(data_len >&＃61; 0);int frame_len &＃61; cal_frame_len(data_len);frame &＃61; new_frame(frame_len);return make_frame(frame.get(), frame_len, tfi, data.get(), data_len);
}int cal_spi_frame_len(int data_len)
{return cal_frame_len(data_len) &＃43; 1;
}int make_spi_frame(uint8_t* buf, int buf_len, uint8_t spi_tfi, uint8_t tfi, const uint8_t* data, int data_len)
{int frame_len &＃61; cal_spi_frame_len(data_len);if (buf &＃61;&＃61; NULL || buf_len &＃61;&＃61; 0){return frame_len;}if (buf_len }int make_spi_frame(frame_ptr& frame, uint8_t spi_tfi, uint8_t tfi, const uint8_t* data, int data_len)
{assert(data_len >&＃61; 0);int frame_len &＃61; cal_spi_frame_len(data_len);frame &＃61; new_frame(frame_len);return make_spi_frame(frame.get(), frame_len, spi_tfi, tfi, data, data_len);
}int make_spi_frame(frame_ptr& frame, uint8_t spi_tfi, uint8_t tfi, data_ptr data, int data_len)
{assert(data_len >&＃61; 0);int frame_len &＃61; cal_spi_frame_len(data_len);frame &＃61; new_frame(frame_len);return make_spi_frame(frame.get(), frame_len, spi_tfi, tfi, data.get(), data_len);
}}


get_uid.cpp

#include
#include
#include
#include
#include
#include
#include "pn532.h"using namespace pn532;#define IOCTL(fd, cmd, arg) \do\{\if (ioctl(fd, cmd, arg) &＃61;&＃61; -1)\{\perror(#cmd);\close(fd);\return -1;\}\}\while(0)void reverse_byte(uint8_t & b)
{uint8_t res &＃61; 0;uint8_t ori &＃61; b;for (int i &＃61; 0; i <8; &＃43;&＃43;i){res <<&＃61; 1;res |&＃61; ori & 0x01;ori >>&＃61; 1;}b &＃61; res;
}void reverse_bits(uint8_t * buf, int len)
{uint8_t* p &＃61; buf;for (int i &＃61; 0; i }int init_spi(const char * dev)
{static const uint8_t spi_mode &＃61; 0;static const uint8_t spi_lsb &＃61; 1;static const uint8_t spi_bpw &＃61; 8;//static const uint32_t spi_speed &＃61; 5000000;static const uint32_t spi_speed &＃61; 1000000;int fd &＃61; open(dev, O_RDWR);if (fd &＃61;&＃61; -1){perror("open spi device:");return -1;}IOCTL(fd, SPI_IOC_WR_MODE, &spi_mode);//IOCTL(fd, SPI_IOC_WR_LSB_FIRST, &spi_lsb);IOCTL(fd, SPI_IOC_WR_BITS_PER_WORD, &spi_bpw);IOCTL(fd, SPI_IOC_WR_MAX_SPEED_HZ, &spi_speed);return fd;
}int sr_spi(int spi, const uint8_t* sendbuf, int sendlen, uint8_t* recvbuf, int recvlen)
{int trnum &＃61; 0;struct spi_ioc_transfer tr[2];memset(tr, 0, sizeof(tr));frame_ptr lsbbuf;if (sendlen > 0){lsbbuf &＃61; new_frame(sendlen);memcpy(lsbbuf.get(), sendbuf, sendlen);reverse_bits(lsbbuf.get(), sendlen);tr[trnum].tx_buf &＃61; (uint64_t)lsbbuf.get();tr[trnum].rx_buf &＃61; 0;tr[trnum].len &＃61; sendlen;&＃43;&＃43;trnum;}if (recvlen > 0){tr[trnum].tx_buf &＃61; 0;tr[trnum].rx_buf &＃61; (uint64_t)recvbuf;tr[trnum].len &＃61; recvlen;&＃43;&＃43;trnum;}if (trnum &＃61;&＃61; 0){return -1;}if (ioctl(spi, SPI_IOC_MESSAGE(trnum), tr) !&＃61; (sendlen &＃43; recvlen)){perror("spi send recv error:");return -1;}if (recvlen > 0){reverse_bits(recvbuf, recvlen);}return sendlen&＃43;recvlen;
}int send_spi(int spi, const uint8_t* sendbuf, int sendlen)
{return sr_spi(spi, sendbuf, sendlen, NULL, 0);
}int recv_spi(int spi, uint8_t* recvbuf, int recvlen)
{return sr_spi(spi, NULL, 0, recvbuf, recvlen);
}void print_hex(const uint8_t * buf, int len)
{const uint8_t * p &＃61; buf;for (int i &＃61; 0; i }int wait_for_ready(int spi)
{static const uint8_t sr[] &＃61; {pn532::SPI_SR};uint8_t buf[1];while (1){usleep(10000);if (sr_spi(spi, sr, 1, buf, 1) !&＃61; 2){printf("spi send recv error!\n");return -1;}if (buf[0] &＃61;&＃61; 0x01)return 0;}return -1;
}#define BUF_SIZE 264int do_cmd(int spi, const uint8_t* cmd, int cmdlen, const char* cmdname, int answerlen)
{static const uint8_t dr[] &＃61; {pn532::SPI_DR};if (cmdname !&＃61; NULL){printf("do command: %s\n", cmdname);}if (answerlen <0){answerlen &＃61; BUF_SIZE;}uint8_t buf[BUF_SIZE];frame_ptr cmd_frame;int cmd_frame_len &＃61; make_spi_frame(cmd_frame, SPI_DW, TFI_H2P, cmd, cmdlen);print_hex(cmd_frame.get(), cmd_frame_len);if (send_spi(spi, cmd_frame.get(), cmd_frame_len) !&＃61; cmd_frame_len){perror("write cmd");return -1;}if (wait_for_ready(spi) !&＃61; 0){return -1;}printf("ready for ack!\n");if (sr_spi(spi, dr, 1, buf, 6) <0){perror("read ack error");return -1;}printf("read ack: ");print_hex(buf, 6);if (wait_for_ready(spi) !&＃61; 0){return -1;}printf("ready for answer!\n");if (sr_spi(spi, dr, 1, buf, answerlen) <0){perror("read answer error");return -1;}printf("read answer: ");print_hex(buf, answerlen);return 0;
}int main(int argc, char *argv[])
{int spi &＃61; init_spi("/dev/spidev0.0");if (spi <0){fprintf(stderr, "init spi device error!\n");return -1;}#if 0uint8_t gfv_data[] &＃61; {0x02};if (do_cmd(spi, gfv_data, sizeof(gfv_data), "get fireware version", 13) <0){return -1;}
#endif#if 1uint8_t set_normal_mode_data[] &＃61; {0x14, 0x01, 0x00, 0x00};if (do_cmd(spi, set_normal_mode_data, sizeof(set_normal_mode_data), "set normal mode", 9) <0){return -1;}
#endif#if 1uint8_t autopoll_data[] &＃61; {0x60, 0xff, 0x02, 0x00, 0x01, 0x02, 0x03, 0x04, 0x10, 0x11, 0x12, 0x20, 0x23};if (do_cmd(spi, autopoll_data, sizeof(autopoll_data), "auto poll", 32) <0){return -1;}
#endif#if 0uint8_t lpt_data[] &＃61; {0x4A, 0x01, 0x00};if (do_cmd(spi, lpt_data, sizeof(lpt_data), "list passive target", 32) <0){return -1;}
#endifclose(spi);return 0;
}


注意&＃xff1a;在使用树莓派测试过程中发现以下问题&＃xff1a;

1. 树莓派的SPI驱动不支持设置LSB传输&＃xff0c;只能以MSB传输&＃xff0c;而PN532模块要求以LSB传输&＃xff0c;所以应用程序只能在发送之前反转位序&＃xff0c;然后发送&＃xff0c;在接收之后反转位序&＃xff0c;然后再处理数据&＃xff1b;

2. PN532用户手册中的以下消息描述不是很清楚&＃xff0c;其中DW&＃xff0c;SR&＃xff0c;DR都应该是主控发给PN532的&＃xff0c;从PN532读到的数据中不包含这些内容。

3. 如果以write写入SR&＃xff0c;以read读取Status&＃xff0c;则大概率会丢失数据导致检测不到ready状态&＃xff0c;所以必须使用ioctl来一次完成写入SR&＃xff0c;读入status&＃xff1b;

4. 如果检测到ready&＃xff0c;但是不读取ack&＃xff0c;程序退出了&＃xff0c;那么下一次运行发送命令后就检测不到ready&＃xff0c;推测PN532按错误处理丢弃了上一次的ACK和本次命令数据&＃xff0c;所以再次运行发送命令后又可以检测到ready&＃xff1b;因此建议在每次程序启动时复位一下PN532模块&＃xff0c;避免之前程序退出遗留了ACK等数据导致程序逻辑错误。

参考

https://blog.csdn.net/TAlice/article/details/83868713
https://www.cnblogs.com/subo_peng/p/4848260.html
https://www.waveshare.net/wiki/PN532_NFC_HAT
https://pinout.xyz/pinout/spi#
https://github.com/nfc-tools/libnfc