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95 lines
3.8 KiB
Python
95 lines
3.8 KiB
Python
# SPI with the Arduino as the master device and the OpenMV Cam as the slave.
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#
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# Please wire up your OpenMV Cam to your Arduino like this:
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#
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# OpenMV Cam Master Out Slave In (P0) - Arduino Uno MOSI (11)
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# OpenMV Cam Master In Slave Out (P1) - Arduino Uno MISO (12)
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# OpenMV Cam Serial Clock (P2) - Arduino Uno SCK (13)
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# OpenMV Cam Slave Select (P3) - Arduino Uno SS (10)
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# OpenMV Cam Ground - Arduino Ground
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import pyb, ustruct, time
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text = "Hello World!\n"
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data = ustruct.pack("<bi%ds" % len(text), 85, len(text), text) # 85 is a sync char.
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# Use "ustruct" to build data packets to send.
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# "<" puts the data in the struct in little endian order.
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# "b" puts a signed char in the data stream.
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# "i" puts a signed integer in the data stream.
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# "%ds" puts a string in the data stream. E.g. "13s" for "Hello World!\n" (13 chars).
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# See https://docs.python.org/3/library/struct.html
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# READ ME!!!
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#
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# Please understand that when your OpenMV Cam is not the SPI master it may miss responding to
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# sending data as a SPI slave no matter if you call "spi.send()" in an interrupt callback or in the
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# main loop below. Because of this you must absolutely design your communications protocol such
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# that if the slave device (the OpenMV Cam) doesn't call "spi.send()" in time that garbage data
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# read from the SPI peripheral by the master (the Arduino) is tossed. To accomplish this we use a
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# sync character of 85 (binary 01010101) which the Arduino will look for as the first byte read.
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# If it doesn't see this then it aborts the SPI transaction and will try again. Second, in order to
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# clear out the SPI peripheral state we always send a multiple of four bytes and an extra four zero
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# bytes to make sure that the SPI peripheral doesn't hold any stale data which could be 85. Note
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# that the OpenMV Cam will miss the "spi.send()" window randomly because it has to service
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# interrupts. Interrupts will happen a lot more while connected to your PC.
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# The hardware SPI bus for your OpenMV Cam is always SPI bus 2.
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# polarity = 0 -> clock is idle low.
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# phase = 0 -> sample data on rising clock edge, output data on falling clock edge.
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spi = pyb.SPI(2, pyb.SPI.SLAVE, polarity=0, phase=0)
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# NSS callback.
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def nss_callback(line):
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global spi, data
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try:
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spi.send(data, timeout=1000)
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except OSError as err:
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pass # Don't care about errors - so pass.
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# Note that there are 3 possible errors. A timeout error, a general purpose error, or
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# a busy error. The error codes are 116, 5, 16 respectively for "err.arg[0]".
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# Configure NSS/CS in IRQ mode to send data when requested by the master.
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pyb.ExtInt(pyb.Pin("P3"), pyb.ExtInt.IRQ_FALLING, pyb.Pin.PULL_UP, nss_callback)
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while(True):
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time.sleep_ms(1000)
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###################################################################################################
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# Arduino Code
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###################################################################################################
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#
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# #include <SPI.h>
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# #define SS_PIN 10
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# #define BAUD_RATE 19200
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# #define CHAR_BUF 128
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#
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# void setup() {
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# pinMode(SS_PIN, OUTPUT);
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# Serial.begin(BAUD_RATE);
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# SPI.begin();
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# SPI.setBitOrder(MSBFIRST);
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# SPI.setClockDivider(SPI_CLOCK_DIV16);
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# SPI.setDataMode(SPI_MODE0);
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# delay(1000); // Give the OpenMV Cam time to bootup.
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# }
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#
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# void loop() {
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# int32_t len = 0;
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# char buff[CHAR_BUF] = {0};
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# digitalWrite(SS_PIN, LOW);
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# delay(1); // Give the OpenMV Cam some time to setup to send data.
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#
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# if(SPI.transfer(1) == 85) { // saw sync char?
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# SPI.transfer(&len, 4); // get length
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# if (len) {
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# SPI.transfer(&buff, min(len, CHAR_BUF));
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# len -= min(len, CHAR_BUF);
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# }
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# while (len--) SPI.transfer(0); // eat any remaining bytes
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# }
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#
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# digitalWrite(SS_PIN, HIGH);
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# Serial.print(buff);
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# delay(1); // Don't loop to quickly.
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# }
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