Apple MultiRam C AUXILIARY, Memory Transfers, Memory Bank Mapping

AUXILIARY MEMORY MANAGEMENT 8.5

An example of a routine to identify useable memory is as follows:

	LDX BANK#	Bank number to start. $1B for //e compatibility
MARKALL	STX BNKSELCT	Select bank with the $C07X bank switch
	STX ALTZP	Write to $C009 for aux. zero page
	STX TEST1	Write the bank number to first location
		in zero page of selected bank
	TXA	Prepare for EOR
	E0R #FF	Reverse the bank’s bits setting
	STA TEST2	Write the checksum byte to second location
		in zero page of selected bank
	DEX	Decrease the bank counter
	BPL MARKALL	Loop through to bank zero
	LDX BANK1	Bank number to start, same as MARKALL start
READALL	STX BNXSELCT	Select bank with the $C07X bank switch
	CPX TEST1	Compare bank number against memory
	BNE MAPFAIL	Memory map marked showing bank n with no memory
	TXA	Prepare for EOR
	EOR #FF	Prepare the checksum for the double check
	CMP TEST2	Compare the EOR’d byte for the double check
	BNE MAPFAIL	Memory map marked showing bank n with no memory
	BEQ MAPPASS	Memory bank exists, mark bank n into memory
READNEXT		MAPFAIL, MAPPASS return here
	DEX	Decrease the bank count
	BPL READALL	Loop through to bank 0
	STX MAINZP	Select main memory zero page
	RTS

Memory Bank Mapping

You should keep a record 0f available memory for your program’s use after you have identified the memory on the card. Either a byte map or a bit map could be used for the memory map. You may wish to construct a map that not only shows which 64K banks are useable, but like DOS and ProDOS sector bit maps, also keeps track of the availability of smaller increments of memory. The auxiliary bank memory map could then become part of a larger memory manager.

You will also need to use a byte or bytes to track the memory bank in current use. The $CO7X strobe cannot be read to see which bank was last called.

Memory Transfers

Data can be transferred from main memory to auxiliary memory and back using standard //c auxiliary memory transfer commands. The RAMRD and RANWRT soft switches and the AUXMOVE routine described in Chapter 7 all function normally. The only difference is the additional need to determine which of the MultiRam C’s 64K banks should be used for the transfer.