extmod/machine_i2c: Use writes not reads in i2c.scan().

deshipu · dpgeorge · commit eaef6b5324fa · 2016-10-11T15:30:46.000+11:00
As per discussion in adafruit#2449, using write requests instead of read requests for I2C.scan() seems to support a larger number of devices, especially ones that are write-only. Even a read-only I2C device has to implement writes in order to be able to receive the address of the register to read.
diff --git a/extmod/machine_i2c.c b/extmod/machine_i2c.c
@@ -272,7 +272,7 @@ STATIC mp_obj_t machine_i2c_scan(mp_obj_t self_in) {
     // 7-bit addresses 0b0000xxx and 0b1111xxx are reserved
     for (int addr = 0x08; addr < 0x78; ++addr) {
         mp_hal_i2c_start(self);
-        int ack = mp_hal_i2c_write_byte(self, (addr << 1) | 1);
+        int ack = mp_hal_i2c_write_byte(self, (addr << 1));
         if (ack) {
             mp_obj_list_append(list, MP_OBJ_NEW_SMALL_INT(addr));
         }

Original file line number	Diff line number	Diff line change
`@@ -272,7 +272,7 @@ STATIC mp_obj_t machine_i2c_scan(mp_obj_t self_in) {`
`272`	`272`	`// 7-bit addresses 0b0000xxx and 0b1111xxx are reserved`
`273`	`273`	`for (int addr = 0x08; addr < 0x78; ++addr) {`
`274`	`274`	`mp_hal_i2c_start(self);`
`275`		`- int ack = mp_hal_i2c_write_byte(self, (addr << 1) \| 1);`
	`275`	`+ int ack = mp_hal_i2c_write_byte(self, (addr << 1));`
`276`	`276`	`if (ack) {`
`277`	`277`	`mp_obj_list_append(list, MP_OBJ_NEW_SMALL_INT(addr));`
`278`	`278`	`}`