USB Improvements

* Introduce shell module for basic serial shell with argument parsing
* Introduce shell_cmd_list module for basic compile-time command
  registration
* Harden USB handling to hang less and drop fewer inputs
  - Service tud_task() with periodic TC0 timer interrupt
  - Service cdc_task() with periodic TC1 timer interrupt
  - Handle shell servicing in main app loop
  - Add a circular buffering layer for reads/writes
* Change newline prints to also send carriage return
* Refactor filesystem commands for shell subsystem
* Introduce new shell commands:
  - 'help' command
  - 'flash' command to reset into bootloader
  - 'stress' command to stress CDC writes

Testing:
* Shell validated on Sensor Watch Blue w/ Linux host
* Shell validated in emscripten emulator
* Tuned by spamming inputs during `stress` cmd until stack didn't crash

1 files changed, 5 insertions, 4 deletions

diff --git a/movement/filesystem.h b/movement/filesystem.h
index 3cd3d092..fa3d9d1a 100644
--- a/movement/filesystem.h
+++ b/movement/filesystem.h
@@ -96,9 +96,10 @@ bool filesystem_write_file(char *filename, char *text, int32_t length);
   */
 bool filesystem_append_file(char *filename, char *text, int32_t length);
 
-/** @brief Handles the interactive file browser when Movement is plugged in to USB.
-  * @param line The command that the user typed into the serial console.
-  */
-void filesystem_process_command(char *line);
+int filesystem_cmd_ls(int argc, char *argv[]);
+int filesystem_cmd_cat(int argc, char *argv[]);
+int filesystem_cmd_df(int argc, char *argv[]);
+int filesystem_cmd_rm(int argc, char *argv[]);
+int filesystem_cmd_echo(int argc, char *argv[]);
 
 #endif // FILESYSTEM_H_