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echo.c
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echo.c
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// Required headers
#include <stdint.h>
#include "echoblob.h"
#include "echo.h"
// Z80 addresses
static volatile uint8_t* const z80_ram = (uint8_t *) 0xA00000;
static volatile uint16_t* const z80_busreq = (uint16_t *) 0xA11100;
static volatile uint16_t* const z80_reset = (uint16_t *) 0xA11200;
// Macros to control the Z80
#define Z80_REQUEST() \
{ *z80_busreq = 0x100; while (*z80_busreq & 0x100); }
#define Z80_RELEASE() \
{ *z80_busreq = 0; }
#define Z80_RESET() \
{ *z80_reset = 0; \
volatile int16_t i; for (i = 4; i >= 0; i--); \
*z80_reset = 0x100; }
// Macro to add delays
// Using volatile is needlessly ugly but at least portable
// GCC is already awful at optimizing, so this isn't that bad...
#define DELAY() \
{ volatile int16_t i; for (i = 0xFF; i >= 0; i--); }
// Look-up tables for echo_set_volume
static const uint8_t fm_volumes[] = {
0x7F,0x7B,0x77,0x73,0x70,0x6C,0x68,0x65,
0x61,0x5E,0x5A,0x57,0x54,0x50,0x4D,0x4A,
0x47,0x44,0x41,0x3F,0x3C,0x39,0x36,0x34,
0x31,0x2F,0x2D,0x2A,0x28,0x26,0x24,0x22,
0x20,0x1E,0x1C,0x1A,0x18,0x16,0x15,0x13,
0x12,0x10,0x0F,0x0D,0x0C,0x0B,0x0A,0x09,
0x08,0x07,0x06,0x05,0x04,0x04,0x03,0x02,
0x02,0x01,0x01,0x01,0x00,0x00,0x00,0x00
};
static const uint8_t psg_volumes[] = {
0x0F,0x0F,0x0E,0x0E,0x0D,0x0D,0x0C,0x0C,
0x0B,0x0B,0x0B,0x0A,0x0A,0x0A,0x09,0x09,
0x08,0x08,0x08,0x07,0x07,0x07,0x06,0x06,
0x06,0x06,0x05,0x05,0x05,0x04,0x04,0x04,
0x04,0x03,0x03,0x03,0x03,0x03,0x02,0x02,
0x02,0x02,0x02,0x02,0x01,0x01,0x01,0x01,
0x01,0x01,0x01,0x01,0x01,0x00,0x00,0x00,
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
};
//***************************************************************************
// echo_init
// Initializes Echo and gets it running.
//---------------------------------------------------------------------------
// param list: pointer to instrument list
//***************************************************************************
void echo_init(const void **list) {
// Take over the Z80
Z80_RESET();
Z80_REQUEST();
// Tell Echo to not run any commands by default (the assembly counterpart
// would tell it to load the instrument list, but we can't do that here
// due to linker shenanigans)
z80_ram[0x1FFF] = 0x00;
// Direct stream is empty yet
z80_ram[0x1F00] = 0xFF;
// Load the instrument list manually, since thanks to linker shenanigans
// we can't implement the list properly in ROM :/
volatile uint8_t *dest = &z80_ram[0x1C00];
while (*list) {
// Retrieve pointer to next instrument
// Cast it to an integer since we need to treat it as such
// This should be considered bad C, but since this is hardware-specific
// code this should be fine to do (portability is not expected)
uint32_t ptr = (uint32_t) *list;
// Turn the pointer into the base+address notation Echo wants and store
// it in Z80 RAM directly (where the list would go)
dest[0x000] = (ptr >> 8 & 0x7F) | 0x80;
dest[0x100] = (ptr & 0xFF);
dest[0x200] = (ptr >> 15 & 0x7F) | (ptr >> 16 & 0x80);
// Go for next pointer
list++;
dest++;
}
// Copy the Echo blob into Z80 RAM
// No, memcpy() won't do here since we must ensure accesses are byte-sized
// (memcpy() may not know this and try word or long accesses)
const uint8_t *src = echo_blob;
dest = z80_ram;
int16_t count = sizeof(echo_blob)-1;
while (count-- >= 0)
*dest++ = *src++;
// Set up global volume
int i;
for (i = 0; i < 12; i++)
z80_ram[0x1FE0+i] = 0;
z80_ram[0x1FEC] = 1;
z80_ram[0x1FF1] = 1;
// Let Echo start running!
Z80_RESET();
Z80_RELEASE();
}
//***************************************************************************
// echo_send_command
// Sends a raw command to Echo. No parameters are taken.
//---------------------------------------------------------------------------
// param cmd: command to send
//***************************************************************************
void echo_send_command(uint8_t cmd) {
// We need access to Z80 bus
Z80_REQUEST();
// Is Echo busy yet?
while (z80_ram[0x1FFF] != 0x00) {
Z80_RELEASE();
DELAY();
Z80_REQUEST();
}
// Write the command
z80_ram[0x1FFF] = cmd;
// Done with the Z80
Z80_RELEASE();
}
//***************************************************************************
// echo_send_command_addr
// Sends a raw command to Echo. An address parameter is taken.
//---------------------------------------------------------------------------
// param cmd: command to send
// param addr: address parameter
//***************************************************************************
void echo_send_command_addr(uint8_t cmd, const void *addr) {
// Since we need to split the address into multiple bytes we put it in an
// integer. This is a bad practice in general, period, but since we don't
// care about portability here we can afford to do it this time.
uint32_t param = (uint32_t) addr;
// We need access to Z80 bus
Z80_REQUEST();
// Is Echo busy yet?
while (z80_ram[0x1FFF] != 0x00) {
Z80_RELEASE();
DELAY();
Z80_REQUEST();
}
// Write the command
z80_ram[0x1FFF] = cmd;
z80_ram[0x1FFD] = param;
param >>= 8;
z80_ram[0x1FFE] = param | 0x80;
param >>= 7;
param = (param & 0x7F) | (param >> 1 & 0x80);
z80_ram[0x1FFC] = param;
// Done with the Z80
Z80_RELEASE();
}
//***************************************************************************
// echo_send_command_byte
// Sends a raw command to Echo. A byte parameter is taken.
//---------------------------------------------------------------------------
// param cmd: command to send
// param byte: parameter
//***************************************************************************
void echo_send_command_byte(uint8_t cmd, uint8_t byte) {
// We need access to Z80 bus
Z80_REQUEST();
// Is Echo busy yet?
while (z80_ram[0x1FFF] != 0x00) {
Z80_RELEASE();
int16_t i;
for (i = 0x3FF; i >= 0; i--);
Z80_REQUEST();
}
// Write the command
z80_ram[0x1FFF] = cmd;
z80_ram[0x1FFC] = byte;
// Done with the Z80
Z80_RELEASE();
}
//***************************************************************************
// echo_play_bgm
// Starts playing background music.
//---------------------------------------------------------------------------
// param ptr: pointer to BGM stream
//***************************************************************************
void echo_play_bgm(const void *ptr) {
echo_send_command_addr(ECHO_CMD_PLAYBGM, ptr);
}
//***************************************************************************
// echo_stop_bgm
// Stops background music playback.
//***************************************************************************
void echo_stop_bgm(void) {
echo_send_command(ECHO_CMD_STOPBGM);
}
//***************************************************************************
// echo_resume_bgm
// Resumes background music playback.
//***************************************************************************
/*
void echo_resume_bgm(void) {
echo_send_command(ECHO_CMD_RESUMEBGM);
}
*/
//***************************************************************************
// echo_play_sfx
// Starts playing a sound effect.
//---------------------------------------------------------------------------
// param ptr: pointer to SFX stream
//***************************************************************************
void echo_play_sfx(const void *ptr) {
echo_send_command_addr(ECHO_CMD_PLAYSFX, ptr);
}
//***************************************************************************
// echo_stop_sfx
// Stops sound effect playback.
//***************************************************************************
void echo_stop_sfx(void) {
echo_send_command(ECHO_CMD_STOPSFX);
}
//***************************************************************************
// echo_play_direct
// Injects events into the BGM stream for the next tick.
//---------------------------------------------------------------------------
// param ptr: pointer to BGM stream
//***************************************************************************
void echo_play_direct(const void *ptr) {
// We need access to Z80 bus
Z80_REQUEST();
// Check where we can start writing events
volatile uint8_t *dest = &z80_ram[0x1F00];
while (*dest != 0xFF) dest++;
// Write the events
const uint8_t *src = (uint8_t*)(ptr);
for (;;) {
uint8_t byte = *src++;
*dest++ = byte;
if (byte == 0xFF) break;
}
// Done with the Z80
Z80_RELEASE();
}
//***************************************************************************
// echo_set_volume
// Changes the global volume for every channel.
//---------------------------------------------------------------------------
// param vol: new volume (0 = quietest, 255 = loudest)
//***************************************************************************
void echo_set_volume(uint8_t vol) {
// We need access to Z80 bus
Z80_REQUEST();
// Set FM volume values
uint8_t fm_vol = fm_volumes[vol >> 2];
z80_ram[0x1FE0] = fm_vol;
z80_ram[0x1FE1] = fm_vol;
z80_ram[0x1FE2] = fm_vol;
z80_ram[0x1FE3] = fm_vol;
z80_ram[0x1FE4] = fm_vol;
z80_ram[0x1FE5] = fm_vol;
z80_ram[0x1FE6] = fm_vol;
z80_ram[0x1FE7] = fm_vol;
// Set PSG volume values
uint8_t psg_vol = psg_volumes[vol >> 2];
z80_ram[0x1FE8] = psg_vol;
z80_ram[0x1FE9] = psg_vol;
z80_ram[0x1FEA] = psg_vol;
z80_ram[0x1FEB] = psg_vol;
// Determine whether to enable PCM
z80_ram[0x1FEC] = (vol >= 0x40) ? 1 : 0;
// Tell Echo to update all the volumes
z80_ram[0x1FF1] = 1;
// Done with the Z80
Z80_RELEASE();
}
//***************************************************************************
// echo_set_volume_ex
// Changes the global volume for each individual channel.
//---------------------------------------------------------------------------
// param ptr: pointer to array with volume values
//***************************************************************************
void echo_set_volume_ex(const uint8_t *ptr) {
// We need access to Z80 bus
Z80_REQUEST();
// Store the new volume values
int i;
for (i = 0; i < 13; i++)
z80_ram[0x1FE0+i] = ptr[i];
// Tell Echo to update all the volumes
z80_ram[0x1FF1] = 1;
// Done with the Z80
Z80_RELEASE();
}
//***************************************************************************
// echo_set_pcm_rate
// Changes the playback rate of PCM.
//---------------------------------------------------------------------------
// param rate: new rate (timer A value)
//***************************************************************************
void echo_set_pcm_rate(uint8_t rate) {
echo_send_command_byte(ECHO_CMD_SETPCMRATE, rate);
}
//***************************************************************************
// echo_get_status
// Retrieves Echo's current status.
//---------------------------------------------------------------------------
// return: status flags (see ECHO_STAT_*)
//***************************************************************************
uint16_t echo_get_status(void) {
// We need access to the Z80
Z80_REQUEST();
// Retrieve status from Z80 RAM
uint16_t status = 0;
status = z80_ram[0x1FF0];
if (z80_ram[0x1FFF] != 0)
status |= ECHO_STAT_BUSY;
if (z80_ram[0x1F00] != 0xFF)
status |= ECHO_STAT_DIRBUSY;
// Done with the Z80
Z80_RELEASE();
// Return status
return status;
}