#ifndef MODBUS_H__
#define MODBUS_H__ 1

/*
 * Loosely modelled after AVR-RS485 by Yoshinori Kohyama (http://algobit.jp/),
 * available at https://github.com/kohyama/AVR-RS485/
 *
 * All bugs by Jan "Yenya" Kasprzak <kas@fi.muni.cz> :-)
 */

/*
 * Call this at the beginning of the program.
 */
void modbus_init(uint8_t unit_id);

/*
 * Call this frequently. Returns 0 when no data was received
 * and the processing went on quickly. Returns 1 after potentially lengthy
 * packet processing.
 */
uint8_t modbus_poll();

typedef enum {
	MB_OK = 0,
	MB_ILLEGAL_FUNC = 1,
	MB_ILLEGAL_ADDR = 2,
	MB_ILLEGAL_VAL  = 3,
} mb_exception;

#define MB_HOLD_REGS_BASE	0	// first register
#define MB_N_HOLD_REGS		80	// total # of registers
#define MB_N_HOLD_REGS_EEPROM	20	// the first N registers eeprom-backed
extern uint16_t hold_regs[MB_N_HOLD_REGS];
#define mb_unit_id	(hold_regs[0])	// MODBUS id in the first register

uint8_t hold_reg_is_valid(uint16_t reg, uint16_t val);

#endif /* MODBUS_H__ */