Merge pull request #404 from pewpew-game/fix-spi-empty-read-write

Allow empty reads and writes for busio.SPI

shared-bindings/bitbangio/I2C.c

@@ -157,6 +157,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(bitbangio_i2c_unlock_obj, bitbangio_i2c_obj_unlock);
 //|
 //|      Read into ``buffer`` from the slave specified by ``address``.
 //|      The number of bytes read will be the length of ``buffer``.
+//|      At least one byte must be read.
 //|
 //|      If ``start`` or ``end`` is provided, then the buffer will be sliced
 //|      as if ``buffer[start:end]``. This will not cause an allocation like
@@ -186,6 +187,9 @@ STATIC mp_obj_t bitbangio_i2c_readfrom_into(size_t n_args, const mp_obj_t *pos_a
     int32_t start = args[ARG_start].u_int;
     uint32_t length = bufinfo.len;
     normalize_buffer_bounds(&start, args[ARG_end].u_int, &length);
+    if (length == 0) {
+        mp_raise_ValueError("Buffer must be at least length 1");
+    }
     uint8_t status = shared_module_bitbangio_i2c_read(self,
                                                       args[ARG_address].u_int,
                                                       ((uint8_t*)bufinfo.buf) + start,
@@ -206,6 +210,9 @@ MP_DEFINE_CONST_FUN_OBJ_KW(bitbangio_i2c_readfrom_into_obj, 3, bitbangio_i2c_rea
 //|      as if ``buffer[start:end]``. This will not cause an allocation like
 //|      ``buffer[start:end]`` will so it saves memory.
 //|
+//|      Writing a buffer or slice of length zero is permitted, as it can be used
+//|      to poll for the existence of a device.
+//|
 //|      :param int address: 7-bit device address
 //|      :param bytearray buffer: buffer containing the bytes to write
 //|      :param int start: Index to start writing from

shared-bindings/bitbangio/SPI.c

@@ -191,6 +191,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(bitbangio_spi_unlock_obj, bitbangio_spi_obj_unlock);
 //|   .. method:: SPI.write(buf)
 //|
 //|     Write the data contained in ``buf``. Requires the SPI being locked.
+//|     If the buffer is empty, nothing happens.
 //|
 // TODO(tannewt): Add support for start and end kwargs.
 STATIC mp_obj_t bitbangio_spi_write(mp_obj_t self_in, mp_obj_t wr_buf) {
@@ -198,6 +199,9 @@ STATIC mp_obj_t bitbangio_spi_write(mp_obj_t self_in, mp_obj_t wr_buf) {
     raise_error_if_deinited(shared_module_bitbangio_spi_deinited(self));
     mp_buffer_info_t src;
     mp_get_buffer_raise(wr_buf, &src, MP_BUFFER_READ);
+    if (src.len == 0) {
+        return mp_const_none;
+    }
     check_lock(self);
     bool ok = shared_module_bitbangio_spi_write(self, src.buf, src.len);
     if (!ok) {
@@ -210,7 +214,9 @@ MP_DEFINE_CONST_FUN_OBJ_2(bitbangio_spi_write_obj, bitbangio_spi_write);
 
 //|   .. method:: SPI.readinto(buf)
 //|
-//|     Read into the buffer specified by ``buf`` while writing zeroes. Requires the SPI being locked.
+//|     Read into the buffer specified by ``buf`` while writing zeroes.
+//|     Requires the SPI being locked.
+//|     If the number of bytes to read is 0, nothing happens.
 //|
 // TODO(tannewt): Add support for start and end kwargs.
 STATIC mp_obj_t bitbangio_spi_readinto(size_t n_args, const mp_obj_t *args) {
@@ -218,6 +224,9 @@ STATIC mp_obj_t bitbangio_spi_readinto(size_t n_args, const mp_obj_t *args) {
     raise_error_if_deinited(shared_module_bitbangio_spi_deinited(self));
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[1], &bufinfo, MP_BUFFER_WRITE);
+    if (bufinfo.len == 0) {
+        return mp_const_none;
+    }
     check_lock(args[0]);
     bool ok = shared_module_bitbangio_spi_read(self, bufinfo.buf, bufinfo.len);
     if (!ok) {

shared-bindings/busio/SPI.c

@@ -207,7 +207,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(busio_spi_unlock_obj, busio_spi_obj_unlock);
 //|   .. method:: SPI.write(buffer, \*, start=0, end=len(buffer))
 //|
 //|     Write the data contained in ``buf``. Requires the SPI being locked.
-//|     At least one byte must be written.
+//|     If the buffer is empty, nothing happens.
 //|
 //|     :param bytearray buffer: buffer containing the bytes to write
 //|     :param int start: Index to start writing from
@@ -233,7 +233,7 @@ STATIC mp_obj_t busio_spi_write(size_t n_args, const mp_obj_t *pos_args, mp_map_
     normalize_buffer_bounds(&start, args[ARG_end].u_int, &length);
 
     if (length == 0) {
-        mp_raise_ValueError("Buffer must be at least length 1");
+        return mp_const_none;
     }
 
     bool ok = common_hal_busio_spi_write(self, ((uint8_t*)bufinfo.buf) + start, length);
@@ -247,8 +247,9 @@ MP_DEFINE_CONST_FUN_OBJ_KW(busio_spi_write_obj, 2, busio_spi_write);
 
 //|   .. method:: SPI.readinto(buffer, \*, start=0, end=len(buffer), write_value=0)
 //|
-//|     Read into the buffer specified by ``buf`` while writing zeroes. Requires the SPI being locked.
+//|     Read into the buffer specified by ``buf`` while writing zeroes.
-//|     At least one byte must be read.
+//|     Requires the SPI being locked.
+//|     If the number of bytes to read is 0, nothing happens.
 //|
 //|     :param bytearray buffer: buffer to write into
 //|     :param int start: Index to start writing at
@@ -276,7 +277,7 @@ STATIC mp_obj_t busio_spi_readinto(size_t n_args, const mp_obj_t *pos_args, mp_m
     normalize_buffer_bounds(&start, args[ARG_end].u_int, &length);
 
     if (length == 0) {
-        mp_raise_ValueError("Buffer must be at least length 1");
+        return mp_const_none;
     }
 
     bool ok = common_hal_busio_spi_read(self, ((uint8_t*)bufinfo.buf) + start, length, args[ARG_write_value].u_int);