Hi Dmitry:

quoted

		if (len < RM_BL_WRT_PKG_SIZE) {
			buf[BL_PKG_IDX] = 4;

Why 4???

4 is trigger index for write flash. Our page write size is 128 bytes, 
but in order to meet maximum I2C bus read/write byte limite and need 
fill full all pages of 128 bytes. So that I split 128 bytes to "4" 
section, and start burning flash if touch MCU get index "4".