Why is reading with the PXA270 UART Windows CE driver slower than expected?

When the bytes received by the PXA270 Windows CE UART driver don't meet or exceed the watermark level, a four byte time delay (2.1 mS at 19.2k baud ) will be incurred for the hardware timeout period as defined by the PXA270 processor User's Guide. Customers can modify the default watermark settings in the driver by adding the following registry key to the corresponding UART in the .reg file of the driver.

"WaterMarker"=dword:1

For example:

[HKEY_LOCAL_MACHINEDriversBuiltInSerial_1]
"Dll"="lpd_pxa270_uart_pxa270_50_0_2_0.dll"
"Prefix"="COM"
"Order"=dword:1
"Index"=dword:2
"DeviceArrayIndex"=dword:80 ; FFUART object
"Irq"=dword:16 ; 22 IRQ_FFUART
"MemBase"=dword:40100000 ; FFUART Register
"MemLen"=dword:40
"IClass"="{CC5195AC-BA49-48a0-BE17-DF6D1B0173DD}"
"WaterMarker"=dword:1

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