When I use a QB8 in place of QY4A the result is a lower internal oscillator speed. A sequence of code that takes 8 seconds to perform in QY4A takes 10.6 seconds if a QB8 is programmed with the same s19 file.
Both QY4A and QB8 devices are programmed with Mon08 Cyclone. Appropriate algorithms used for each device. Proper oscillator trimming is done.
I know that the code in the QY4A is running at the correct speed. I have measured the actual speed at 3.8 MHz. So for whatever reason, the QB8 has a speed of about 2.86 MHz. running the same code.
I went through the memory maps to make sure the QY4A code would "drop straight in" which it looks to me it does. The oscillator sections of both devices data sheets look to be identical and all QY4A registers have the same addresses as QB8.
The bulk of the development of this application was done using mmevs with QBLTY daughter board emulating QB8. In mmevs the timing is the same as in actual QY4A device.
So what am I missing folks? It's got to be something simple.