USB example code, high RAM usage

[ktallevi]

So I took the sample ex_usb_hid program (from version 4.068), and compiled it for the PIC18F87J50.

RAM usage is at %75! This does not leave much room for the rest of my application as it requires more than %25 of the RAM. Any way to bring this USB-related RAM usage down without changing microcontrollers?

thanks

[Ttelmah]

You can reduce the RAM usage, by reducing the number of endpoints allocated. The big 'reason', is that when USB is not implemented, there is a huge lump of RAM available for 'normal use', in the area used for the USB buffers. As soon as you implement USB, a large amount of this RAM, is immediately used by the hardware, depending on the number of endpoints in use, and the size allocated for each. The default is to allocate only three endpoints on the 18F2450/4450, but 16 on the 87J chips. Look in the PIC18_usb.h file, where this is all configured. On these, all the RAM, -1280 bytes, is allocated for the USB buffer, which is where it is mainly going. You can fairly easily halve the default RAM usage on these chips, but still expect to use something like 40%...

Best Wishes

[bwhiten]

You can lower the USB buffer memory allocation in the pic18_usb.h
file.
Change line 166 like this:
was:

[ktallevi]

thanks guys, RAM usage is down to %15, exactly what I needed!

[Ttelmah]

Be careful. At '15%', expect a fairly massive performance hit. This is why I mentioned 40%, which still gave full performance for me...

Best Wishes