WIP: Add bitbanging I2C driver.

drivers/i2c-bitbang/i2c.py

@@ -0,0 +1,130 @@
+import sys
+import utime
+from machine import Pin
+
+
+class I2C:
+
+    def __init__(self, sda, scl):
+        self.sda = sda
+        self.scl = scl
+        self.sda.init(Pin.IN)
+        self.scl.init(Pin.IN)
+        self.sda(0)
+        self.scl(0)
+
+    def sda_high(self):
+        self.sda.init(Pin.IN)
+
+    def sda_low(self):
+        self.sda.init(Pin.OUT)
+
+    def scl_high(self):
+        self.scl.init(Pin.IN)
+
+    def scl_low(self):
+        self.scl.init(Pin.OUT)
+
+    def delay(self):
+        utime.sleep_us(5)
+
+    def start(self):
+        self.sda_low()
+        self.delay()
+        self.scl_low()
+        self.delay()
+
+    def restart(self):
+        self.sda_high();
+        self.delay();
+        self.scl_high();
+        self.delay();
+        self.start();
+
+    def stop(self):
+        self.sda_low();
+        self.scl_high();
+        self.delay();
+        self.sda_high();
+        self.delay();
+
+    def readbit(self):
+        self.sda_high();
+        self.scl_high();
+        self.delay();
+        bit = self.sda();
+        self.scl_low();
+        return bit
+
+    def writebit(self, val):
+        if val:
+            self.sda_high();
+        else:
+            self.sda_low();
+        self.delay();
+        self.scl_high();
+        self.delay(); # Rather should sense scl for clock stretching
+        self.scl_low();
+
+    def writebyte(self, b):
+        for i in range(8):
+            self.writebit(b & 0x80);
+            b <<= 1;
+        return self.readbit();
+
+    def readbyte(self, ack=True):
+        b = 0;
+        for i in range(8):
+            b <<= 1;
+            b |= self.readbit()
+        self.writebit(not ack);
+        return b
+
+    def mem_write(self, data, i2c_addr, mem_addr):
+        self.start()
+        print(i2c.writebyte(i2c_addr << 1))
+        print(i2c.writebyte(mem_addr))
+        for b in data:
+            print(i2c.writebyte(b))
+        self.stop()
+
+    def mem_read(self, sz, i2c_addr, mem_addr):
+        self.start()
+        print(i2c.writebyte(i2c_addr << 1))
+        print(i2c.writebyte(mem_addr))
+        self.restart()
+        print(i2c.writebyte((i2c_addr << 1) | 1))
+        res = b""
+        while sz:
+            sz -= 1
+            ack = bool(sz)
+            b = self.readbyte(ack)
+            res += bytes([b])
+        self.stop()
+        return res
+
+# Accelerometer needs to be powered on first. Even
+# though signal is called "AVDD", and there's separate
+# "DVDD", without AVDD, it won't event talk on I2C bus.
+accel_pwr = Pin("MMA_AVDD")
+accel_pwr.value(1)
+
+sda = Pin("X10", Pin.IN)
+scl = Pin("X9", Pin.IN)
+i2c = I2C(sda, scl)
+
+i2c.start()
+print("presence:", i2c.writebyte(0x4c << 1))
+i2c.stop()
+
+ACCEL_ADDR = 0x4c
+ACCEL_AXIS_X_REG = 0
+ACCEL_MODE_REG = 7
+
+# Now activate measurements
+i2c.mem_write(b"\x01", ACCEL_ADDR, ACCEL_MODE_REG)
+
+while 1:
+    val = i2c.mem_read(1, ACCEL_ADDR, ACCEL_AXIS_X_REG)
+    print(val)
+    utime.sleep(1)