Make flash_do_cmd public (#269)

* Make flash_do_cmd public

* Fix typo in comment

src/rp2_common/hardware_flash/flash.c

@@ -123,9 +123,7 @@ static void __no_inline_not_in_flash_func(flash_cs_force)(bool high) {
     );
 }
 
-// May want to expose this at some point but this is unlikely to be the right
-// interface to do so. Keep it static
-static void __no_inline_not_in_flash_func(flash_do_cmd)(const uint8_t *txbuf, uint8_t *rxbuf, size_t count) {
+void __no_inline_not_in_flash_func(flash_do_cmd)(const uint8_t *txbuf, uint8_t *rxbuf, size_t count) {
     void (*connect_internal_flash)(void) = (void(*)(void))rom_func_lookup(rom_table_code('I', 'F'));
     void (*flash_exit_xip)(void) = (void(*)(void))rom_func_lookup(rom_table_code('E', 'X'));
     void (*flash_flush_cache)(void) = (void(*)(void))rom_func_lookup(rom_table_code('F', 'C'));

src/rp2_common/hardware_flash/include/hardware/flash.h

@@ -80,6 +80,22 @@ void flash_range_program(uint32_t flash_offs, const uint8_t *data, size_t count)
  */
 void flash_get_unique_id(uint8_t *id_out);
 
+/*! \brief Execute bidirectional flash command
+ *  \ingroup hardware_flash
+ *
+ * Execute a bidirectional command to the flash. Bytes are simultaneously
+ * transmitted and received. Therefore, both buffers must be the same length,
+ * count, which is the length of the overall transaction. This is useful for
+ * reading metadata from the flash chip. Do *NOT* use it to mutate the data
+ * stored on the flash because it will not flush the cache.
+ *
+ *  \param txbuf Pointer to a byte buffer which will be transmitted to the flash
+ *  \param rxbuf Pointer to a byte buffer where data received from the flash will be written
+ *  \param count Length in bytes of txbuf and of rxbuf
+ */
+void flash_do_cmd(const uint8_t *txbuf, uint8_t *rxbuf, size_t count);
+
+
 #ifdef __cplusplus
 }
 #endif