mirror of
https://github.com/RevCurtisP/C02.git
synced 2024-06-01 05:41:34 +00:00
121 lines
5.3 KiB
Plaintext
121 lines
5.3 KiB
Plaintext
Template Functions for C02 Programs
|
|
|
|
This module provides functions to read from and write to extended
|
|
memory.
|
|
|
|
Extended memory is RAM that is not directly addressable by the 6502.
|
|
Read and write operations use a 24-bit logical address, which is
|
|
comprised of an 8-bit bank and 16-bit offset and automatically updated
|
|
after each operation.
|
|
|
|
At the beginning of the program use the directives
|
|
|
|
#include <stddef.h02>
|
|
#include <xmemory.h02>
|
|
|
|
The following functions are defined:
|
|
|
|
b,d = xgetad(); Returns the current logical extended bank b
|
|
and offset d.
|
|
|
|
Note: the physical address stored in XMBANK
|
|
and XMADDR is converted to a logical bank and
|
|
offset, which are returned.
|
|
|
|
xsetad(b,d); Sets the current logical extended bank to b
|
|
and offset to d.
|
|
|
|
This extended address is used for all read and
|
|
write functions except for the page operations.
|
|
|
|
Note: the logical address is converted to a
|
|
physical address stored in XMBANK and XMADDR.
|
|
|
|
c = xgetc(); Reads a byte from the current extended address,
|
|
increments the address, and returns the byte
|
|
as c.
|
|
|
|
xputc(c); Writes byte c to the current extended address,
|
|
then increments the address.
|
|
|
|
w = xgeti(); Reads a word starting at the current extended
|
|
address, adds 2 to the address, and returns the
|
|
word as w.
|
|
|
|
xputi(w); Writes word w at the current extended address,
|
|
then adds 2 to the address.
|
|
|
|
c,w = xgetl(); Reads a long starting at the current extended
|
|
address, adds 3 to the address, and returns the
|
|
high byte of the long in c and the low word in w.
|
|
|
|
xputl(c,w); Writes the long consisting of the byte c and
|
|
word w at the current extended address, then
|
|
adds 3 to the address.
|
|
|
|
xread(n,r); Reads n bytes starting at the current extended
|
|
address into array r, then adds n to the address.
|
|
|
|
xwrite(n,r); Writes n bytes of array r starting at the current
|
|
extended address, then adds n to the address.
|
|
|
|
xswap(n,r); Swaps n bytes of array r with n bytes starting at
|
|
the current extended address, then adds n to the
|
|
address.
|
|
|
|
xload(w); Reads word w bytes into local memory starting at
|
|
the address specified by a call to setdst() from
|
|
extended memory starting at the current extended
|
|
address, then adds w to the address.
|
|
|
|
xsave(w); Writes word w bytes from local memory starting at
|
|
the address specified by a call to setsrc() into
|
|
extended memory starting at the current extended
|
|
address, then adds w to the address.
|
|
|
|
xchng(w); Swaps word w bytes in local memory starting at
|
|
the address specified by a call to setdst() with
|
|
extended memory starting at the current extended
|
|
address, then adds w to the address.
|
|
|
|
xsetpg(b,p) Sets the current extended address to bank b and
|
|
offset p * 256. This ensures that the address is
|
|
on a page boundary for subsequent page read and
|
|
write operations.
|
|
|
|
Note: The page operation are the fastest of the
|
|
block read and write functions since the code
|
|
can use indirect addressing.
|
|
|
|
xrpage(n,p); Copies n 256 byte pages starting at the current
|
|
extended bank and page to local memory starting
|
|
at address p * 256, then updates the extended
|
|
address accordingly.
|
|
|
|
xwpage(n,p); Copies n 256 bytes from local memory starting
|
|
at address p * 256 to extended memory starting at
|
|
current bank and page, then updates the extended
|
|
address accordingly.
|
|
|
|
xspage(n,p); Swaps n 256 bytes from local memory starting at
|
|
address p * 256 with extended memory starting at
|
|
current bank and page, then updates the extended
|
|
address accordingly.
|
|
|
|
Note: This library expects the following functions to be defined:
|
|
|
|
getdst(); Get Destination Pointer
|
|
getsrc(); Get Source Pointer
|
|
resrxy(); Restore X and Y Registers
|
|
savrxy(); Save X and Y Registers
|
|
|
|
along with the zero page variables
|
|
|
|
dstptr,srcptr: Destination and Source Pointer
|
|
|
|
and the external variables
|
|
|
|
xmaddr,xmbank; Extended Memory Address and Bank
|
|
temp1,temp2: Temporary storage
|
|
|