[Lcd4linux-devel] Time-out for picoLCD 256x64

[Martin Z. <co...@mz...>]

Hello everybody,

I had written that polling the button states using LCD::GPI(1)
considerably slows down output on my picoLCD 256x64 and located the
problem in this function:

   static int drv_pLG_read(unsigned char *data, int size)
   {
     return usb_interrupt_read(lcd, USB_ENDPOINT_IN + 1, (char *) data,
     size, 1000);
   }

On second thoughts, I have made the mistake to think that this function
times out *every* time.  When a key is pressed, however, the function
exits directly and thus only times out when no data are present for
usb_interrupt_read().

This means that the time-out value is *much* too high.  The driver 
usually waits a *full second* for key data before going on and doing 
(more important) things like updating the LCD.  As this makes the 
display rather unresponsive, I think that the time-out value should be 
changed.

My problem is that I don't know what time-out value should be used.  I
have experimented a little: 1 ms is too low, while 2 ms work fine on my
desktop.  On my embedded system, 3 ms are needed.  But what about people
using the display with an old USB 1.0 port?  I propose 5 ms or 10 ms --
what do you think?

Thanks,

Martin
-- 
www.mzuther.de
www.radix-musik.de