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[fireflyP] SPI使用
发表于 2016-7-28 11:53:36
浏览：39520
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本帖最后由 zhansb 于 2016-8-25 09:23 编辑
模块安装请参考：http://developer.t-firefly.com/thread-10503-1-2.html
fireflyP的SPI使用spidev接口，所以使用前，必须确保内核已经支持spidev（可参考补丁或者下载现成的固件）。
在python中使用help(Spi)可以打印Spi使用的方法，主要的接口有：
| read(self, length, speed=0, bits_per_word=0, delay=0)
| Perform half-duplex Spi read as a binary string
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| Args:
| length: Integer count of words to read
| speed: Optional temporary bitrate override in Hz. 0 (default)
| uses existing spidev speed setting.
| bits_per_word: Optional temporary bits_per_word override. 0
| (default) will use the current bits_per_word setting.
| delay: Optional delay in usecs between sending the last bit and
| deselecting the chip select line. 0 (default) for no delay.
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| Returns:
| List of words read from device
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| transfer(self, data, speed=0, bits_per_word=0, delay=0)
| Perform full-duplex Spi transfer
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| Args:
| data: List of words to transmit
| speed: Optional temporary bitrate override in Hz. 0 (default)
| uses existing spidev speed setting.
| bits_per_word: Optional temporary bits_per_word override. 0
| (default) will use the current bits_per_word setting.
| delay: Optional delay in usecs between sending the last bit and
| deselecting the chip select line. 0 (default) for no delay.
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| Returns:
| List of words read from Spi bus during transfer
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| write(self, data, speed=0, bits_per_word=0, delay=0)
| Perform half-duplex Spi write.
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| Args:
| data: List of words to write
| speed: Optional temporary bitrate override in Hz. 0 (default)
| uses existing spidev speed setting.
| bits_per_word: Optional temporary bits_per_word override. 0
| (default) will use the current bits_per_word setting.
| delay: Optional delay in usecs between sending the last bit and
| deselecting the chip select line. 0 (default) for no delay.
SPI使用的流程如下：
1.初始化SPI设备，如spi = Spi('/dev/spidev0.0')
2.设置SPI的参数，比如speed，bits_per_word，mode等，也可以在初始化SPI时作为关键字参数传入
3.然后就可以开始读写SPI了，如spi.write([0x12, 0x34, 0xAB, 0xCD])、received = spi.read(10)
目前Firefly-RK3288目前支持的SPI配置参数有：mode、speed、bits_per_word、cs_high、loop，不支持lsb_first、no_cs等参数的设置
下面用介绍一下怎么使用fireflyP中的SPI点亮OLED屏：
笔者手上刚好有个0.96寸的OLED显示屏：
OLED与开发板的接线如下：
| OLED | Firefly-RK3288 | | GND=电源地 | GND | | VCC=电源 | 5V | | D0=时钟 | SPI0 CLK | | D1=数据 | SPI0 TXD | | RST=复位 | GPIO0A7 | | DC=数据/命令 | GPIO7B1 | | CS=片选 | SPI0 CSN0 |
OLED的demo代码在github上的demo/spi_test.py，我们来分析一下Oled的代码：
__init__(self, dev, pin_rst, pin_dc)函数主要是做SPI设备、RST和DC的初始化并通过SPI写入OLED初始化的指令。其中SPI设备初始化相关的有：
- self._spi = Spi(dev)
- self._spi.mode = Spi.MODE_3
- self._spi.bits_per_word = 8
- self._spi.speed = 1000*1000
初始完SPI和GPIO后，接下来就可以使用SPI写入指令，写了个封装的接口_write，由于Firefly-RK3288目前不支持lsb_first，需要软件转换LSB和MSB（相关代码：tbuf=int(bin(tbuf)[2:].zfill(8)[::-1], 2)）
OLED写指令用下面的接口：
- self._write(reg,Oled.WR_CMD)
- self._write(data,Oled.WR_DATA)
Oled也封装了一些显示接口：
| draw_bitmap(self, bitmap, x, y, w, h)
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| draw_char(self, x, y, ch)
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| draw_line(self, x0, y0, x1, y1)
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| draw_point(self, x, y)
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| draw_str(self, x, y, s)
因此我们可以在Oled上直接使用以上接口显示：
- $ cd pyFireflyP/demo/
- $ sudo python
- >>> from spi_test import Oled,BM_FIREFLY
- >>> oled = Oled("/dev/spidev0.0", 'GPIO0A7', 'GPIO7B1')
- >>> oled.draw_str(2,1, 'Hello,Firefly!')
- >>> oled.draw_bitmap(BM_FIREFLY, 44,16, 40, 48)
- >>> oled.draw_line(1,1,128,1)
- >>> oled.draw_line(1,1,1,64)
- >>> oled.draw_line(128,1,128,64)
- >>> oled.draw_line(1,64,128,64)
- $ sudo python spi_test.py
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