diff --git a/hw/esp.c b/hw/esp.c
index b698a43..9ab41ba 100644
--- a/hw/esp.c
+++ b/hw/esp.c
@@ -45,6 +45,7 @@
 
 struct ESPState {
     SysBusDevice busdev;
+    MemoryRegion iomem;
     uint8_t rregs[ESP_REGS];
     uint8_t wregs[ESP_REGS];
     qemu_irq irq;
@@ -504,7 +505,8 @@
     }
 }
 
-static uint32_t esp_mem_readb(void *opaque, target_phys_addr_t addr)
+static uint64_t esp_mem_read(void *opaque, target_phys_addr_t addr,
+                             unsigned size)
 {
     ESPState *s = opaque;
     uint32_t saddr, old_val;
@@ -545,7 +547,8 @@
     return s->rregs[saddr];
 }
 
-static void esp_mem_writeb(void *opaque, target_phys_addr_t addr, uint32_t val)
+static void esp_mem_write(void *opaque, target_phys_addr_t addr,
+                          uint64_t val, unsigned size)
 {
     ESPState *s = opaque;
     uint32_t saddr;
@@ -641,7 +644,7 @@
             s->rregs[ESP_RINTR] = 0;
             break;
         default:
-            ESP_ERROR("Unhandled ESP command (%2.2x)\n", val);
+            ESP_ERROR("Unhandled ESP command (%2.2x)\n", (unsigned)val);
             break;
         }
         break;
@@ -656,22 +659,23 @@
         s->rregs[saddr] = val;
         break;
     default:
-        ESP_ERROR("invalid write of 0x%02x at [0x%x]\n", val, saddr);
+        ESP_ERROR("invalid write of 0x%02x at [0x%x]\n", (unsigned)val, saddr);
         return;
     }
     s->wregs[saddr] = val;
 }
 
-static CPUReadMemoryFunc * const esp_mem_read[3] = {
-    esp_mem_readb,
-    NULL,
-    NULL,
-};
+static bool esp_mem_accepts(void *opaque, target_phys_addr_t addr,
+                            unsigned size, bool is_write)
+{
+    return (size == 1) || (is_write && size == 4);
+}
 
-static CPUWriteMemoryFunc * const esp_mem_write[3] = {
-    esp_mem_writeb,
-    NULL,
-    esp_mem_writeb,
+static const MemoryRegionOps esp_mem_ops = {
+    .read = esp_mem_read,
+    .write = esp_mem_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+    .valid.accepts = esp_mem_accepts,
 };
 
 static const VMStateDescription vmstate_esp = {
@@ -735,14 +739,13 @@
 static int esp_init1(SysBusDevice *dev)
 {
     ESPState *s = FROM_SYSBUS(ESPState, dev);
-    int esp_io_memory;
 
     sysbus_init_irq(dev, &s->irq);
     assert(s->it_shift != -1);
 
-    esp_io_memory = cpu_register_io_memory(esp_mem_read, esp_mem_write, s,
-                                           DEVICE_NATIVE_ENDIAN);
-    sysbus_init_mmio(dev, ESP_REGS << s->it_shift, esp_io_memory);
+    memory_region_init_io(&s->iomem, &esp_mem_ops, s,
+                          "esp", ESP_REGS << s->it_shift);
+    sysbus_init_mmio_region(dev, &s->iomem);
 
     qdev_init_gpio_in(&dev->qdev, esp_gpio_demux, 2);