This adds the MPAGE (sdcc _XPAGE) SFR, which is used by sdcc in `--xstack`
mode to provide the upper byte of the address for `MOVX A, @Ri` and
`MOVX @Ri, A` instructions.
Classic 8051 uses the P2 SFR value for this, but the RTL IP block does not
seem to be using the "Port 2 module".
From the databook:
```
To replace the function of the Port 2 latch in designs that do not use a
Port 2 module, the DW8051 provides an additional special function register,
MPAGE, at SFR address 92h. During MOVX A, @Ri and MOVX @Ri, A instructions,
the DW8051 places the contents of the MPAGE register on the upper 8 address
bits (mem_addr[15:8]). This provides the paging function that is normally
provided by the Port 2 latch. The MPAGE register has no function when a
Port 2 module is used to connect external RAM.
```
Downside of Timer0 is, we have to manually reload
the timer value. Timer2 can do that automaticly.
This saves a lot of time in the interrupt-handler
of the Timer.
Currently Timer2 is used for baudrate-generation
but in a separete commit this is moved to Timer1.
Fix several bugs found in the write-flash code during installer coding.
Move all flash functions into CODE0. This is required to share these
functions with the installer image (currently they are duplicated so
they are not within the CODE1 segment).
De-magics all Flash command codes based on the Winbond W25Q32JV
datasheet.
So instead do it manual split a uint16_t in to two uint8_t.
The compiler can do it, so reduces user error.
Note: compiler writes the lower/LSB part first.
When that is importent this can´t be used.
Assembly is still the same except note above.
Tobias Diedrich
René van Dorst
logicog