ePOS2 SDK：如何保持与打印机的连接处于活动状态？

Question

I am using ePOS2 SDK from Epson to communicate with receipt printer TM-M30.
I am able to successfully connect to printer and print some data.
After finishing printing I am keeping connection to printer, so next time I need to print something I don't connect to it again.

However connection is alive for only 90 seconds. After 90 seconds of inactivity connection printer is dropped and Epos2Printer notifies delegate that power is off:

func onPtrStatusChange(_ printerObj: Epos2Printer, eventType: Int32) {
    let eventStatus = Epos2StatusEvent(rawValue: eventType)
    // Event status is EPOS2_EVENT_POWER_OFF here
}

I don't see any parameters for Epos2Printer to keep connection alive.

Does anybody know how force printer to keep connection beyond 90 seconds?

Answer 1

Turned out Epos2Printer uses TCP connection to communicate with printer and TCP itself drops connection in 90 seconds.
To avoid this I am sending signal to empty printer port for cash drawer after 85 seconds of inactivity:

printer.addPulse(EPOS2_DRAWER_5PIN.rawValue, time: EPOS2_PULSE_100.rawValue)
printer.beginTransaction()
printer.sendData(Int(EPOS2_PARAM_DEFAULT))
printer.endTransaction()
printer.clearCommandBuffer()