Add "User Bus" module.

This new module allows the connection of custom peripherals to the
computer bus. This module can be used to implement user's mods.

Author: giomba

CMakeLists.txt

@@ -25,6 +25,7 @@ set(CORE_SRCS
     src/time.c
     src/timer.c
     src/tokenizer.c
+    src/ubus.c
     src/upd8255.c
     src/video.c
     src/ram/auxram.c

src/ubus.c

@@ -0,0 +1,88 @@
+#include "ubus.h"
+
+#include "conf.h"
+
+#include <stddef.h>
+#include <string.h>
+
+#define UBUS_MAX_PERIPHERALS (4)
+
+#define LOG_LEVEL LOG_LVL_INFO
+#include "log.h"
+
+struct ubus_io_slot {
+    ceda_ioaddr_t base;
+    uint32_t top;
+    ubus_io_read_t in;
+    ubus_io_write_t out;
+};
+
+static struct ubus_io_slot ubus_slots[UBUS_MAX_PERIPHERALS];
+static size_t ubus_used = 0;
+
+void ubus_init(CEDAModule *mod) {
+    memset(mod, 0, sizeof(*mod));
+
+    mod->init = ubus_init;
+}
+
+bool ubus_register(ceda_ioaddr_t base, uint32_t top, ubus_io_read_t read,
+                   ubus_io_write_t write) {
+    if (!read && !write)
+        return false;
+
+    if (top > 0x100)
+        return false;
+
+    if (top <= base)
+        return false;
+
+    if (ubus_used == UBUS_MAX_PERIPHERALS) {
+        LOG_WARN("Too many peripherals registered\n");
+        return false;
+    }
+
+    // check if peripherals are overlapping
+    for (size_t i = 0; i < ubus_used; ++i) {
+        struct ubus_io_slot *slot = &ubus_slots[i];
+        if (slot->base >= base && slot->base < top)
+            return false;
+        if (slot->top <= top && slot->top > base)
+            return false;
+        if (slot->base < base && slot->top > top)
+            return false;
+        if (slot->base > base && slot->top < top)
+            return false;
+    }
+
+    ubus_slots[ubus_used].base = base;
+    ubus_slots[ubus_used].top = top;
+    ubus_slots[ubus_used].in = read;
+    ubus_slots[ubus_used].out = write;
+    ubus_used += 1;
+
+    LOG_INFO("Registered peripheral at %02x\n", (unsigned int)base);
+
+    return true;
+}
+
+zuint8 ubus_io_in(ceda_ioaddr_t address) {
+    for (size_t i = 0; i < ubus_used; ++i) {
+        struct ubus_io_slot *slot = &ubus_slots[i];
+        if (address >= slot->base && address < slot->top)
+            if (slot->in)
+                return slot->in(address - slot->base);
+    }
+    return 0;
+}
+
+void ubus_io_out(ceda_ioaddr_t address, uint8_t value) {
+    for (size_t i = 0; i < ubus_used; ++i) {
+        struct ubus_io_slot *slot = &ubus_slots[i];
+        if (address >= slot->base && address < slot->top)
+            if (slot->out) {
+                slot->out(address - slot->base, value);
+                return;
+            }
+    }
+}

src/ubus.h

@@ -0,0 +1,37 @@
+#ifndef CEDA_USER_BUS_H
+#define CEDA_USER_BUS_H
+
+#include "module.h"
+#include "type.h"
+
+#include <stdbool.h>
+
+#include <Z80.h>
+
+typedef uint8_t (*ubus_io_read_t)(ceda_ioaddr_t address);
+typedef void (*ubus_io_write_t)(ceda_ioaddr_t address, uint8_t value);
+
+/**
+ * @brief Initialize the User Bus module.
+ *
+ * This module allows users to connect custom peripherals to the computer bus.
+ */
+void ubus_init(CEDAModule *mod);
+
+/**
+ * @brief Register a peripheral on the bus.
+ *
+ * @param base Peripheral base address.
+ * @param top Peripheral top address + 1 (eg. the first unused address)
+ * @param read IO input callback.
+ * @param write IO output callback.
+ *
+ * @return true in case of success, false otherwise.
+ */
+bool ubus_register(ceda_ioaddr_t base, uint32_t top, ubus_io_read_t read,
+                   ubus_io_write_t write);
+
+zuint8 ubus_io_in(ceda_ioaddr_t address);
+void ubus_io_out(ceda_ioaddr_t address, uint8_t value);
+
+#endif // CEDA_USER_BUS_H