/* tapecart - a tape port storage pod for the C64 * * Copyright (C) 2013-2017 Ingo Korb * All rights reserved. * Idea by enthusi * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * * loader.asm: Two-bit fastloader for the C64 tape port * * Translated to C "macro assembler" by Ingo Korb */ #define ASMARG_16BIT(value) (value) & 0xff, ((value) >> 8) & 0xff #define ASM_and_imm(val) 0x29, (val) #define ASM_bcc(offset) 0x90, (offset & 0xff) #define ASM_bit_zp(addr) 0x24, (addr) #define ASM_bne(offset) 0xd0, (offset & 0xff) #define ASM_clc 0x18 #define ASM_cli 0x58 #define ASM_cmp_zp(addr) 0xc5, (addr) #define ASM_cpx_zp(addr) 0xe4, (addr) #define ASM_dex 0xca #define ASM_dey 0x88 #define ASM_eor_zp(addr) 0x45, (addr) #define ASM_inc_zp(addr) 0xe6, (addr) #define ASM_inx 0xe8 #define ASM_iny 0xc8 #define ASM_jmp_ind(addr) 0x6c, ASMARG_16BIT(addr) #define ASM_jsr(addr) 0x20, ASMARG_16BIT(addr) #define ASM_lda_imm(val) 0xa9, (val) #define ASM_lda_zp(addr) 0xa5, (addr) #define ASM_ldx_imm(val) 0xa2, (val) #define ASM_ldx_zp(addr) 0xa6, (addr) #define ASM_ldy_imm(val) 0xa0, (val) #define ASM_lsr 0x4a #define ASM_nop 0xea #define ASM_ora_abs_x(addr) 0x1d, ASMARG_16BIT(addr) #define ASM_ora_imm(val) 0x09, (val) #define ASM_rol_abs(addr) 0x2e, ASMARG_16BIT(addr) #define ASM_ror_abs(addr) 0x6e, ASMARG_16BIT(addr) #define ASM_rts 0x60 #define ASM_sec 0x38 #define ASM_sei 0x78 #define ASM_sta_abs_x(addr) 0x99, ASMARG_16BIT(addr) #define ASM_sta_ind_y(addr) 0x91, (addr) #define ASM_sta_zp(addr) 0x85, (addr) #define ASM_stx_zp(addr) 0x86, (addr) #define ASM_sty_zp(addr) 0x84, (addr) #define ASM_tax 0xaa #define LOADER_CALLADDR 0xaa #define LOADER_ENDADDR 0xac #define LOADER_LOADADDR 0xae #define LOADER_INFO_BLOCK_ADDR LOADER_CALLADDR #define LOADER_INFO_BLOCK_SIZE 6 #define LOADER_SUB_GETBYTE 0x03b2 #define LOADER_NIBBLETAB 0x03e3 /* * = $0351 */ ASM_ror_abs(0xd011), /* blank screen */ ASM_sei, ASM_clc, ASM_ldy_imm(16), /* 16 bits */ ASM_ldx_imm(0), ASM_stx_zp(0xc6), /* clear keyboard buffer */ /*handshake_loop:*/ ASM_lda_imm(0x27), /* motor off, write low */ ASM_rol_abs(0x03f3), /* read top bit of signature byte (handshk) */ ASM_bcc(2), /* skip next instruction */ ASM_ora_imm(0x08), /* set write high */ ASM_sta_zp(0x01), /* delay loop because motor line is heavily RC-filtered */ ASM_dex, ASM_nop, ASM_bne(-4), ASM_and_imm(0xdf), /* motor on, keep write */ ASM_sta_zp(0x01), /* another delay loop, turning motor on is faster */ ASM_dex, ASM_bne(-3), ASM_dey, ASM_bne(-25), /* to handshake_loop until all bits are sent */ ASM_lda_imm(0x30), /* motor off, write low, all RAM */ ASM_sta_zp(0x01), /* read info block */ ASM_ldy_imm(256 - LOADER_INFO_BLOCK_SIZE), /* [037b] info_loop:*/ ASM_jsr(LOADER_SUB_GETBYTE), ASM_sta_abs_x(LOADER_INFO_BLOCK_ADDR - (256 - LOADER_INFO_BLOCK_SIZE)), ASM_iny, ASM_bne(-9), /* to info_loop */ /* [0384] data_loop:*/ ASM_jsr(LOADER_SUB_GETBYTE), ASM_sta_ind_y(LOADER_LOADADDR), ASM_inc_zp(LOADER_LOADADDR), ASM_bne(2), /* skip high-inc if no overflow */ ASM_inc_zp(LOADER_LOADADDR + 1), /* check if at end of file */ ASM_lda_zp(LOADER_LOADADDR), ASM_cmp_zp(LOADER_ENDADDR), ASM_bne(-17), /* to data_loop */ ASM_ldx_zp(LOADER_LOADADDR + 1), ASM_cpx_zp(LOADER_ENDADDR + 1), ASM_bne(-23), /* to data_loop */ /* load complete, fix system state and start */ ASM_ldy_imm(0x37), /* turn on ROMs */ ASM_sty_zp(0x01), ASM_sec, ASM_rol_abs(0xd011), /* un-blank screen */ ASM_stx_zp(0x2e), /* update BASIC pointers */ ASM_stx_zp(0x30), ASM_sta_zp(0x2d), ASM_sta_zp(0x2f), ASM_cli, ASM_jsr(0xe453), /* restore vectors */ ASM_jmp_ind(LOADER_CALLADDR), /* [03b2] getbyte -- returns byte in A, preserves Y */ /* wait until tapecart is ready (sense low) */ ASM_lda_imm(0x10), ASM_bit_zp(0x01), ASM_bne(-4), /* signal ready-ness */ ASM_ldx_imm(0x38), ASM_lda_imm(0x27), ASM_stx_zp(0x01), /* set write high */ ASM_sta_zp(0x00), /* 3 - switch write to input */ ASM_nop, /* 2 - delay */ /* receive byte */ ASM_lda_zp(0x01), /* 3 - read bits 5+4 */ ASM_and_imm(0x18), /* 2 - mask */ ASM_lsr, /* 2 - shift down */ ASM_lsr, /* 2 */ ASM_eor_zp(0x01), /* 3 - read bits 7+6 */ ASM_lsr, /* 2 */ ASM_and_imm(0x0f), /* 2 - mask */ ASM_tax, /* 2 - remember value */ ASM_lda_zp(0x01), /* 3 - read bits 1+0 */ ASM_and_imm(0x18), /* 2 - mask */ ASM_lsr, /* 2 - shift down */ ASM_lsr, /* 2 */ ASM_eor_zp(0x01), /* 3 - read bits 3+2 */ ASM_lsr, /* 2 */ ASM_and_imm(0x0f), /* 2 - mask */ ASM_ora_abs_x(LOADER_NIBBLETAB), /* 4 - add upper nibble */ ASM_ldx_imm(0x2f), /* 2 - switch write to output */ ASM_stx_zp(0x00), /* 3 */ ASM_inx, /* set write low again */ ASM_stx_zp(0x01), ASM_rts, /*nibbletab:*/ 0x00, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70, 0x80, 0x90, 0xa0, 0xb0, 0xc0, 0xd0, 0xe0, 0xf0, /*handshk:*/ 0xca /* handshake value seed */