Allow empty reads and writes for busio.SPI

This is mostly for convenience, so that user code doesn't
need to add additional checks.

Also, bring the bitbangio into compatibility with busio wrt. empty
buffers.

1 files changed, 6 insertions, 5 deletions

diff --git a/shared-bindings/busio/SPI.c b/shared-bindings/busio/SPI.c
index add541aa7..72787af30 100644
--- a/shared-bindings/busio/SPI.c
+++ b/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.
-//|     At least one byte must be read.
+//|     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.
 //|
 //|     :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);