bank_test.c

/*
 * ZX Spectrum Next z88dk banking example 
 */

#include <arch/zxn.h>           // ZX Spectrum Next architecture specfic functions
#include <stdint.h>             // standard names for ints with no ambiguity 
#include <input.h>
#include <stdio.h>
#include <z80.h>

#include "bank_test.h"

/*
 * The ZX Spectrum Next physical memory is split into banks
 *
 * The Next supports two bank sizes
 * The classic 16K bank scheme and the Next specific 8K bank scheme
 * In the Next scheme each 16k bank is subdivided into two 8k banks
 *
 * The ZX Spectrum z80 processor can only address 64k. 
 * 
 * For the classic the 16k bank scheme the visible 64K address space is split into 4 * 16K slots
 * By default
 * slot 1 (0x000)     contains the ROM 
 * slot 2 (0x4000)    contains BANK 5 (normally used for the ULA screen)
 * slot 3 (0x8000)    contains BANK 2 (free RAM)
 * slot 4 (0xc000)    contains BANK 0 (free RAM) 
 * 
 * The classic 128K spectrum style banking scheme can only alter the 16k bank mapped into slot 4 (0xc000)
 * Banks 0, 1, 2, 3, 4, 5, 7 can be mapped into slot 4
 * 
 * For the Next 8k banking scheme the visible 64K address spaces is split into 8 * 8k slotes
 * By default these slots mirror the classic scheme and the bank numbers are based on the 8k sizes 
 * For example 16k slot 2 contains 8k banks 10 and 11
 * 
 * The 8k-bank accessed in an 8k-slot is selected by writing the 8k-bank number to bits 7-0 of the 8 Next registers from Memory management slot 0 bank ($50) upwards 
 * $50 addresses 8k-slot 0, $51 addresses 8k-slot 1, and so on.
 *
 * In addition, in 8k-slots 0 and 1 only, the ROM can be paged in by selecting the otherwise nonexistent 8k-page $FF. 
 * Whether the high or the low 8k of the ROM is mapped is determined by which 8k-slot is used. 
 * 
 * To compile C code into a specific bank you need to 
 * a) set the ORG address for slot the bank will be paged into within the C code
 * b) tell the compiler to compile the code into the correct bank (physical memory location)
 *
 * To set the org address within a C file use #pragma output CRT_ORG_CODE
 * For example #pragma output CRT_ORG_CODE = 0xC000
 * This applies to the scope of the file
 * 
 * To compile the code into the correcty bank use the --codeseg and --constseg options e.g. to compile code into a specified bank
 * ZXN banks are named as BANK_0 (16k) BANK_0_L (8k) BANK_0_H (8k) BANK_1 (16k) etc
 * See https://github.com/z88dk/z88dk/blob/0cb51ee64b02bfc08645026dd141f671c0de6dc9/lib/target/zxn/classic/memory_map.asm
 * For example to complile to 16k bank 0 zcc +zxn -vn -c -SO3 -compiler sdcc -clib=sdcc_iy  --codesegBANK_0 --constsegBANK_0 -o ./obj/bank_test_0.o src/bank_test_0.c
 * 
 * By default the stack is set at the top of memory in 16k slot 4
 * In the classic 128k banking scheme, if we want to swap a different 16k bank into slot 4 we have to move the stack out of the way 
 * Use #pragma output REGISTER_SP to move the stack elsewhere
 * It can be moved to the top of bank 5 with #pragma output REGISTER_SP = 0xbfff
 * 
 * To call a function in a bank the bank must be manually paged into the visible 64k memory address space
 * The C compiler does not do this automatically for you
 * There are banking features in the z88dk compiler but these do not support the ZX Spectrum Next target out of the box?
 * Examples of how to page a bank into memory
 * 
 * Classic 128k - page 16k bank 1 into slot 4 (0xc00)
 * #include <z80.h>
 * z80_outp(0x7ffd, 1);
 * 
 * ZXN - page 8k bank 2 into slot 6 (0xc00)
 * ZXN_WRITE_REG(0x56, 2);
 * ZXN_WRITE_MMU6(2);
 * Remember 8k banks numbers are 2x and 2x+1 the 16k bank number e.g. 16k bank 1 = 8k banks 2 & 3
 * 
 * 
 * To compile the example
 * zcc +zxn -vn -c -SO3 -compiler sdcc -clib=sdcc_iy -pragma-include:zpragma.inc -o bank_test.o bank_test.c
 * zcc +zxn -vn -c -SO3 -compiler sdcc -clib=sdcc_iy  --codesegBANK_0 --constsegBANK_0 -o bank_test_0.o bank_test_0.c
 * zcc +zxn -vn -c -SO3 -compiler sdcc -clib=sdcc_iy  --codesegBANK_1_L --constsegBANK_1_L -o bank_test_1.o bank_test_1.c
 * zcc +zxn -vn -c -SO3 -compiler sdcc -clib=sdcc_iy  --codesegBANK_1 --constsegBANK_1 -o bank_test_1.o bank_test_1.c
 * zcc +zxn -vn -clib=sdcc_iy  -startup=1 bank_test.o bank_test_0.o bank_test_1.o -pragma-include:zpragma.inc -o bank_test.nex -create-app -subtype=nex
 * 
 * NB bank 0 is merged into the main memory bank as the main memory bank includes 5, 2, 0 by default
*/

#pragma output REGISTER_SP = 0xbfff

int main()
{
    printf("Printing from main\n");
    test_bank0(10);

    
    //GLOBAL_ZXN_PORT_7FFD = 1;

    z80_outp(0x7ffd, 1);

    //ZXN_WRITE_REG(0x56, 2);
    //ZXN_WRITE_MMU6(2);

    test_bank1(8);


    while(1)
    {
        //loop
     };

    return 0;
}