+ // Iterate though coke slots and find the first one with a drink avaliable
+ // `giCoke_NextCokeSlot` ensures that the slots rotate
+ for( int i = 0; i < 4; i ++ )
+ {
+ int slot = 6 + (i + giCoke_NextCokeSlot) % 4;
+ if( !Coke_int_IsSlotEmpty(slot) )
+ {
+ if(bDispensing) {
+ giCoke_NextCokeSlot ++;
+ if(giCoke_NextCokeSlot == 4) giCoke_NextCokeSlot = 0;
+ }
+ return slot; // Drink avaliable
+ }
+ }
+
+ // Coke is empty!
+ // - Return 6, even if it's empty, the checks elsewhere will avoid problems
+ return 6;
+}
+
+int Coke_int_IsSlotEmpty(int Slot)
+{
+ uint8_t status;
+
+ if( Slot < 0 || Slot > 9 ) return -1;
+
+ if(!gCoke_Modbus)
+ return -2;
+
+ errno = 0;
+ if( modbus_read_bits(gCoke_Modbus, ciCoke_StatusBitBase + Slot, 1, &status) <= 0 )
+ {
+ // TODO: Retry connection, or fail
+ perror("Coke_int_IsSlotEmpty - modbus_read_bits");
+ return -2;
+ }
+
+ return status == 0;
+}
+
+int Coke_int_DropSlot(int Slot)
+{
+ uint8_t res;
+
+ if(Slot < 0 || Slot > 9) return -1;
+
+ // Can't dispense if the machine is not connected
+ if( !gCoke_Modbus )
+ return -2;
+
+ // Check if a dispense is in progress
+ if( modbus_read_bits(gCoke_Modbus, ciCoke_DropBitBase + Slot, 1, &res) <= 0 )
+ {
+ perror("Coke_int_DropSlot - modbus_read_bits#1");
+ return -2;
+ }
+ if( res != 0 )
+ {
+ // Manual dispense in progress
+ return -1;
+ }
+
+ // Dispense
+ if( modbus_write_bit(gCoke_Modbus, ciCoke_DropBitBase + Slot, 1) < 0 )
+ {
+ perror("Coke_int_DropSlot - modbus_write_bit");
+ return -2;
+ }
+
+ // Check that it started
+ usleep(1000); // 1ms
+ if( modbus_read_bits(gCoke_Modbus, ciCoke_DropBitBase + Slot, 1, &res) <= 0 )
+ {
+ perror("Coke_int_DropSlot - modbus_read_bits#2");
+ return -2;
+ }
+ if( res == 0 )
+ {
+ // Oops!, no drink
+ return 1;
+ }