esp8266: Implement bit-bang I2C read, and add i2c.readfrom method.

I2C reading tested with TSL2561 luminosity sensor.

esp8266/modpybi2c.c

@@ -186,6 +186,52 @@ er:
     nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "I2C bus error"));
 }
 
+STATIC int mphal_i2c_read_byte(pyb_i2c_obj_t *self, uint8_t *val) {
+    mphal_i2c_wait_a();
+    mphal_i2c_set_scl(self, 0);
+    mphal_i2c_wait_a();
+
+    uint8_t dat = 0;
+    for (int i = 7; i >= 0; i--) {
+        mphal_i2c_set_scl(self, 1);
+        mphal_i2c_wait_a();
+        dat = (dat << 1) | mphal_i2c_get_sda(self);
+        mphal_i2c_wait_a();
+        mphal_i2c_set_scl(self, 0);
+        mphal_i2c_wait_a();
+    }
+    *val = dat;
+
+    mphal_i2c_wait_a();
+    mphal_i2c_set_scl(self, 1);
+    mphal_i2c_wait_a();
+    mphal_i2c_wait_b();
+    mphal_i2c_set_scl(self, 0);
+    mphal_i2c_wait_a();
+
+    return 1; // success
+}
+
+STATIC void mphal_i2c_read(pyb_i2c_obj_t *self, uint8_t addr, uint8_t *data, size_t len, bool stop) {
+    mphal_i2c_start(self);
+    if (!mphal_i2c_write_byte(self, (addr << 1) | 1)) {
+        goto er;
+    }
+    while (len--) {
+        if (!mphal_i2c_read_byte(self, data++)) {
+            goto er;
+        }
+    }
+    if (stop) {
+        mphal_i2c_stop(self);
+    }
+    return;
+
+er:
+    mphal_i2c_stop(self);
+    nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "I2C bus error"));
+}
+
 /******************************************************************************/
 // MicroPython bindings for I2C
 
@@ -219,6 +265,26 @@ STATIC mp_obj_t pyb_i2c_obj_init(mp_uint_t n_args, const mp_obj_t *args, mp_map_
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(pyb_i2c_init_obj, 1, pyb_i2c_obj_init);
 
+STATIC mp_obj_t pyb_i2c_readfrom(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    enum { ARG_addr, ARG_n, ARG_stop };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_addr, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
+        { MP_QSTR_n,    MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
+        { MP_QSTR_stop, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = true} },
+    };
+    pyb_i2c_obj_t *self = pos_args[0];
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    // do the I2C transfer
+    vstr_t vstr;
+    vstr_init_len(&vstr, args[ARG_n].u_int);
+    mphal_i2c_read(self, args[ARG_addr].u_int, (uint8_t*)vstr.buf, vstr.len, args[ARG_stop].u_bool);
+
+    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
+}
+MP_DEFINE_CONST_FUN_OBJ_KW(pyb_i2c_readfrom_obj, 1, pyb_i2c_readfrom);
+
 STATIC mp_obj_t pyb_i2c_writeto(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     enum { ARG_addr, ARG_buf, ARG_stop };
     static const mp_arg_t allowed_args[] = {
@@ -243,6 +309,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_i2c_writeto_obj, 1, pyb_i2c_writeto);
 
 STATIC const mp_rom_map_elem_t pyb_i2c_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_init),    MP_ROM_PTR(&pyb_i2c_init_obj) },
+    { MP_ROM_QSTR(MP_QSTR_readfrom), MP_ROM_PTR(&pyb_i2c_readfrom_obj) },
     { MP_ROM_QSTR(MP_QSTR_writeto), MP_ROM_PTR(&pyb_i2c_writeto_obj) },
 };
 

esp8266/qstrdefsport.h

@@ -148,10 +148,12 @@ Q(init)
 Q(scl)
 Q(sda)
 Q(freq)
+Q(readfrom)
 Q(writeto)
 Q(stop)
 Q(buf)
 Q(addr)
+Q(n)
 
 // utime
 Q(utime)