Improve print state machine, add print API

src/ltp1245.h

@@ -1,14 +1,23 @@
 #pragma once
 
 #include <stdbool.h>
+#include <string.h>
 
 #include "stm32f1xx.h"
 
-typedef int (*LTP1245_DataProvider_t)(uint8_t *buffer);
+typedef enum
+{
+    LTP1245_OK,
+    LTP1245_NO_PAPER,
+    LTP1245_HEAD_UP
+} LTP1245_Result_t;
 
 #define LTP1245_MAX_DRIVE_FREQ  473     // In Hz
 #define LTP1245_BUFFER_LINES    64
+#define LTP1245_LINEWIDTH       384     // In pixels
 
 #define LTP1245_TH_REXT         10      // In kΩ
 
 void LTP1245_Init(void);
+LTP1245_Result_t LTP1245_FeedPaper(int lines);
+LTP1245_Result_t LTP1245_Print(uint8_t *data, int lines);