149 lines
4.2 KiB
C
149 lines
4.2 KiB
C
#include "nes.h"
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//=================================================================================================
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//
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// NES operations
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// This file includes all the nes functions possible to be called from the nes dictionary.
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//
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// See description of the commands contained here in shared/shared_dictionaries.h
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//
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//=================================================================================================
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/* Desc:Function takes an opcode which was transmitted via USB
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* then decodes it to call designated function.
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* shared_dict_nes.h is used in both host and fw to ensure opcodes/names align
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* Pre: Macros must be defined in firmware pinport.h
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* opcode must be defined in shared_dict_nes.h
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* Post:function call complete.
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* Rtn: SUCCESS if opcode found, ERR_UNKN_NES_OPCODE_24BOP if opcode not present.
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*/
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uint8_t nes_opcode_24b_operand( uint8_t opcode, uint8_t addrH, uint8_t addrL, uint8_t data )
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{
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switch (opcode) {
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case DISCRETE_EXP0_PRGROM_WR:
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discrete_exp0_prgrom_wr( addrH, addrL, data );
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break;
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default:
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//macro doesn't exist
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return ERR_UNKN_NES_OPCODE_24BOP;
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}
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return SUCCESS;
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}
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/* Desc:Function takes an opcode which was transmitted via USB
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* then decodes it to call designated function.
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* shared_dict_nes.h is used in both host and fw to ensure opcodes/names align
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* Pre: Macros must be defined in firmware pinport.h
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* opcode must be defined in shared_dict_nes.h
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* Post:pointer to data updated with return value.
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* Rtn: SUCCESS if opcode found, ERR_UNKN_NES_OPCODE_16BOP_8BRV if opcode not present.
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*/
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uint8_t nes_opcode_16b_operand_8b_return( uint8_t opcode, uint8_t addrH, uint8_t addrL, uint8_t *data )
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{
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switch (opcode) {
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case EMULATE_NES_CPU_RD:
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*data = emulate_nes_cpu_rd( addrH, addrL );
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break;
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default:
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//macro doesn't exist
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return ERR_UNKN_NES_OPCODE_16BOP_8BRV;
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}
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return SUCCESS;
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}
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/* Desc: Discrete board PRG-ROM only write, does not write to mapper
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* PRG-ROM /WE <- EXP0 w/PU
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* PRG-ROM /OE <- /ROMSEL
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* PRG-ROM /CE <- GND
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* PRG-ROM write: /WE & /CE low, /OE high
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* mapper '161 CLK <- /ROMSEL
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* mapper '161 /LOAD <- PRG R/W
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* mapper '161 /LOAD must be low on rising edge of CLK to latch data
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* This is a /WE controlled write with data latched on rising edge EXP0
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* Note:addrH bit7 has no effect (ends up on PPU /A13)
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* /ROMSEL, M2, & PRG R/W signals untouched
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* Pre: nes_init() setup of io pins
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* Post:data latched by PRG-ROM, mapper register unaffected
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* address left on bus
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* data left on bus, but pullup only
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* EXP0 left pulled up
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* Rtn: None
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*/
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void discrete_exp0_prgrom_wr( uint8_t addrH, uint8_t addrL, uint8_t data )
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{
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_DATA_OP();
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DATA_OUT = addrH;
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_AHL_CLK(); //addrH latched
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DATA_OUT = data;
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ADDR_OUT = addrL;
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_EXP0_LO(); //Tas = 0ns, Tah = 30ns
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_EXP0_PU(); //Twp = 40ns, Tds = 40ns, Tdh = 0ns
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//16Mhz avr clk = 62.5ns period guarantees timing reqts
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//Need to check with scope to make sure EXP0 P/U effective
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_DATA_IP();
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}
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/* Desc:Emulate NES CPU Read as best possible
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* decode A15 from addrH to set /ROMSEL as expected
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* float EXP0
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* toggle M2 as NES would
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* insert some NOP's in to be slow like NES
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* Note:not the fastest read operation
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* Pre: nes_init() setup of io pins
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* Post:address left on bus
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* data bus left clear
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* EXP0 left floating
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* Rtn: None
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*/
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uint8_t emulate_nes_cpu_rd( uint8_t addrH, uint8_t addrL )
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{
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uint8_t read; //return value
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//m2 should be low as it aids in disabling WRAM
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//this is also m2 state at beginging of CPU cycle
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//all these pins should already be in this state, but
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//go ahead and setup just to be sure since we're trying
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//to be as accurate as possible
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_EXP0_FLT(); //this could have been left pulled up
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_M2_LO(); //start of CPU cycle
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_ROMSEL_HI(); //trails M2
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_PRGRW_RD(); //happens just after M2
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//set address bus
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ADDR_OUT = addrL;
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_ADDRH_SET(addrH);
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//couple NOP's to wait a bit
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NOP();
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NOP();
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//set M2 and /ROMSEL
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if( addrH >= 0x80 ) { //addressing cart rom space
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_M2_HI();
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_ROMSEL_LO(); //romsel trails M2 during CPU operations
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} else {
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_M2_HI();
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}
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//couple more NOP's waiting for data
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NOP();
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NOP();
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NOP();
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NOP();
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//latch data
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read = DATA_IN;
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//return bus to default
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_M2_LO();
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_ROMSEL_HI();
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return read;
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}
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