Multiplexer Driver Developer’s Guide
8 Known Problems
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8 Known Problems
8.1Booting Operating System
Windows 2000 and Windows XP toggle the signals of the serial interfaces. As a result, the module will be switched on, even if the WinMux2 driver is not active. The driver accesses the connected module only when the virtual ports are accessed.
If the WinMux2k driver is used by accessing one or more of the virtual ports, it switches off the module when the last virtual port is closed again. Only TC45 and XC18 do not switch off in this case.
8.2Shutdown of the Operating System
If the supported operating system has been installed in ACPI mode, the power supply will be automatically switched off. This power down might cause pulses on those signals of the serial interfaces which are responsible for switching the module on. This may happen, even if it had correctly switched off before by the driver.
If the module has its own power supply it might stay switched on after the shutdown procedure of the computer has completed.
8.3Standby of the Operating System
If the operating system has been installed in ACPI mode, it supports improved power management by also send- ing computer components into suspend mode. The serial WinMux2k driver supports this power management by switching the module into standby mode, if the driver is in use by accessing one or more of the virtual ports. If the operating system has been properly configured together with the BIOS, incoming calls or real clock alarms wake the operating system up again. During this wake up the first characters sent by the module to the operating system via the serial interface are lost. This is no restriction of the serial WinMux2k driver, but caused by the operating system.
E.g. in case of an incoming call the first RING event is lost. Usually this causes no problem because the RING is repeated every few seconds. However, in case of the real clock alarm the module only sends one CALA URC. As a result, the URC will not be indicated though the alarm will be correctly executed.
Additionally, in some cases when the computer switches to suspend mode, this causes pulses on the serial inter- face signals which wake up the module again.
8.4Wake on Ring
If the operating system is in standby mode and the module has not been switched off, incoming calls and real time clock alarms should wake up the operating system (wake on RING). This feature belongs to the ACPI power management mechanisms which are not properly implemented on all PC systems. It is independent of the mul- tiplexer driver. When the ring signal toggles on the serial interface like on incoming calls and real time clock alarms, this should wake up the operating system, if the PC has been properly configured. On some systems not the RING signal but data transferred to the PC (the “RING” or “CALA” messages from the module) wake up the operating system.
To avoid loss of data the multiplexer driver switches on the hardware flow control on the module. This means that the module cannot send data to the PC, if the operating system is in standby mode and therefore the serial interface is blocked by the hardware flow control. As a consequence the operating system does not wake up, if the system ignores the RING signal, because the module cannot send the “RING” or “CALA” messages to the PC.
Mux_Drv_DevGuide_v07 | Page 35 of 36 | |
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