210 lines
9.0 KiB
C
210 lines
9.0 KiB
C
/*****************************************************************************/
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/* */
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/* peripherals.c */
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/* */
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/* Memory-mapped peripheral subsystem for the 6502 simulator */
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/* */
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/* */
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/* */
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/* (C) 2024-2025, Sidney Cadot */
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/* */
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/* */
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/* This software is provided 'as-is', without any expressed or implied */
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/* warranty. In no event will the authors be held liable for any damages */
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/* arising from the use of this software. */
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/* */
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/* Permission is granted to anyone to use this software for any purpose, */
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/* including commercial applications, and to alter it and redistribute it */
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/* freely, subject to the following restrictions: */
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/* */
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/* 1. The origin of this software must not be misrepresented; you must not */
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/* claim that you wrote the original software. If you use this software */
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/* in a product, an acknowledgment in the product documentation would be */
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/* appreciated but is not required. */
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/* 2. Altered source versions must be plainly marked as such, and must not */
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/* be misrepresented as being the original software. */
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/* 3. This notice may not be removed or altered from any source */
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/* distribution. */
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/* */
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/*****************************************************************************/
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#include <stdbool.h>
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#include <time.h>
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#if defined(__MINGW64__)
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/* For gettimeofday() */
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#include <sys/time.h>
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#endif
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#include "peripherals.h"
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/*****************************************************************************/
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/* Data */
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/*****************************************************************************/
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/* The system-wide state of the peripherals */
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Sim65Peripherals Peripherals;
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/*****************************************************************************/
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/* Code */
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/*****************************************************************************/
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static bool GetWallclockTime (struct timespec * ts)
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/* Get the wallclock time with nanosecond resolution. */
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{
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/* Note: the 'struct timespec' type is available on all compilers we want to support. */
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bool time_valid;
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#if defined(__MINGW64__)
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/* When using the MinGW64 compiler, neither timespec_get() nor clock_gettime()
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* are available; using either of them makes the Linux workflow build fail.
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* The gettimeofday() function does work, so use that; its microsecond resolution
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* is fine for most applications.
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*/
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struct timeval tv;
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time_valid = (gettimeofday(&tv, NULL) == 0);
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if (time_valid) {
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ts->tv_sec = tv.tv_sec;
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ts->tv_nsec = tv.tv_usec * 1000;
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}
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#elif defined(_MSC_VER)
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/* Using the Microsoft C++ compiler.
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* clock_gettime() is not available; use timespec_get() instead.
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*/
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time_valid = timespec_get(ts, TIME_UTC) == TIME_UTC;
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#else
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/* On all other compilers, assume that clock_gettime() is available.
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* This is true on Linux and MacOS, at least.
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*/
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time_valid = clock_gettime(CLOCK_REALTIME, ts) == 0;
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#endif
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return time_valid;
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}
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void PeripheralsWriteByte (uint8_t Addr, uint8_t Val)
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/* Write a byte to a memory location in the peripherals address aperture. */
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{
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switch (Addr) {
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/* Handle writes to the Counter peripheral. */
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_LATCH: {
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/* A write to the "latch" register performs a simultaneous latch of all registers. */
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/* Latch the current wallclock time before doing anything else. */
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struct timespec ts;
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bool time_valid = GetWallclockTime (&ts);
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if (time_valid) {
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/* Wallclock time: number of nanoseconds since 1-1-1970. */
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Peripherals.Counter.LatchedWallclockTime = 1000000000 * (uint64_t)ts.tv_sec + ts.tv_nsec;
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/* Wallclock time, split: high word is number of seconds since 1-1-1970,
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* low word is number of nanoseconds since the start of that second. */
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Peripherals.Counter.LatchedWallclockTimeSplit = (uint64_t)ts.tv_sec << 32 | ts.tv_nsec;
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} else {
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/* Unable to get time. Report max uint64 value for both fields. */
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Peripherals.Counter.LatchedWallclockTime = -1;
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Peripherals.Counter.LatchedWallclockTimeSplit = -1;
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}
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/* Latch the counters that reflect the state of the processor. */
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Peripherals.Counter.LatchedClockCycles = Peripherals.Counter.ClockCycles;
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Peripherals.Counter.LatchedCpuInstructions = Peripherals.Counter.CpuInstructions;
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Peripherals.Counter.LatchedIrqEvents = Peripherals.Counter.IrqEvents;
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Peripherals.Counter.LatchedNmiEvents = Peripherals.Counter.NmiEvents;
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break;
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}
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_SELECT: {
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/* Set the value of the visibility-selection register. */
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Peripherals.Counter.LatchedValueSelected = Val;
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break;
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}
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/* Handle writes to unused and read-only peripheral addresses. */
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default: {
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/* No action. */
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}
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}
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}
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uint8_t PeripheralsReadByte (uint8_t Addr)
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/* Read a byte from a memory location in the peripherals address aperture. */
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{
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switch (Addr) {
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/* Handle reads from the Counter peripheral. */
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_SELECT: {
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return Peripherals.Counter.LatchedValueSelected;
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}
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 0:
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 1:
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 2:
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 3:
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 4:
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 5:
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 6:
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case PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE + 7: {
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/* Read from any of the eight counter bytes.
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* The first byte is the 64 bit value's LSB, the seventh byte is its MSB.
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*/
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unsigned SelectedByteIndex = Addr - PERIPHERALS_COUNTER_ADDRESS_OFFSET_VALUE; /* 0 .. 7 */
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uint64_t Value;
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switch (Peripherals.Counter.LatchedValueSelected) {
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case PERIPHERALS_COUNTER_SELECT_CLOCKCYCLE_COUNTER: Value = Peripherals.Counter.LatchedClockCycles; break;
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case PERIPHERALS_COUNTER_SELECT_INSTRUCTION_COUNTER: Value = Peripherals.Counter.LatchedCpuInstructions; break;
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case PERIPHERALS_COUNTER_SELECT_IRQ_COUNTER: Value = Peripherals.Counter.LatchedIrqEvents; break;
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case PERIPHERALS_COUNTER_SELECT_NMI_COUNTER: Value = Peripherals.Counter.LatchedNmiEvents; break;
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case PERIPHERALS_COUNTER_SELECT_WALLCLOCK_TIME: Value = Peripherals.Counter.LatchedWallclockTime; break;
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case PERIPHERALS_COUNTER_SELECT_WALLCLOCK_TIME_SPLIT: Value = Peripherals.Counter.LatchedWallclockTimeSplit; break;
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default: Value = 0; /* Reading from a non-existent latch register will yield 0. */
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}
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/* Return the desired byte of the latched counter; 0==LSB, 7==MSB. */
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return (uint8_t)(Value >> (SelectedByteIndex * 8));
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}
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/* Handle reads from unused peripheral and write-only addresses. */
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default: {
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/* Return zero value. */
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return 0;
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}
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}
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}
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void PeripheralsInit (void)
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/* Initialize the peripherals. */
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{
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/* Initialize the Counter peripheral */
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Peripherals.Counter.ClockCycles = 0;
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Peripherals.Counter.CpuInstructions = 0;
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Peripherals.Counter.IrqEvents = 0;
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Peripherals.Counter.NmiEvents = 0;
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Peripherals.Counter.LatchedClockCycles = 0;
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Peripherals.Counter.LatchedCpuInstructions = 0;
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Peripherals.Counter.LatchedIrqEvents = 0;
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Peripherals.Counter.LatchedNmiEvents = 0;
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Peripherals.Counter.LatchedWallclockTime = 0;
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Peripherals.Counter.LatchedWallclockTimeSplit = 0;
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Peripherals.Counter.LatchedValueSelected = 0;
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}
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