How to Program the Wonderswan's Real Time Clock (e.g. w/ Wonderwitch)
v0.1

by zalas

Overview:

The RTC for the Wonderswan contains information about the current date/time, etc.

Ports:

0xCA - this is the command port, when commands get written here, they get executed immediately
	when read, this port will yield an asserted high bit for acknowledgement, the argument
	byte must be in 0xCB upon writing a command to 0xCA or else it will miss it
0xCB - this is the data port, for passing arguments and for reading, etc.

Commands:

0x10 - Reset

Write 0x10 to port 0xCA
Wait for ACK from 0xCA

0x12 - Write Timer Settings

Write timer setting byte to 0xCB
Write 0x12 to port 0xCA
Wait for ACK from 0xCA

0x13 - Read Timer Settings

Write 0x13 to port 0xCA
Wait for ACK from 0xCA
Read timer settings byte from 0xCB

0x14 - Set Time/Date

Write first byte of time/date structure into 0xCB
Write 0x14 into 0xCA
Wait for ACK
Write second byte into 0xCB
Wait for ACK
repeat until all 7 bytes have been entered

0x15 - Get Time/Date

Write 0x15 into 0xCA
Wait for ACK
Read byte from 0xCB
Repeat above 2 steps 7 times

Data Structure:

Time Settings Byte:
MSB  LSB
xwaxxxxx
	w - should always be set?
	a - should be set to enable RTC alarm (in addition to interrupt enable)

Time/Date Structure (all of the following fields are in BCD format)

0000 - Year (in addition to 2000)
0001 - Month
0002 - Day
0003 - Day of the Week
0004 - Hour (high bit denotes PM, e.g. 0x00 to 0x11 for 00:00 to 11:00 and 0x92 to 0xA3 for 12:00 to 23:00)
0005 - Minute
0006 - Second