Handout

arch/ioport.h

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+/*! \file
+ *  \brief \ref IOPort provides access to the x86 IO address space
+ */
+
+#pragma once
+#include "../types.h"
+
+/*! \brief Abstracts access to the I/O address space
+ *
+ *  x86 PCs have a separated I/O address space that is accessible only via the
+ * machine instructions `in` and `out`. An IOPort object encapsulates the
+ * corresponding address in the I/O address space and can be used for byte or
+ *  word-wise reading or writing.
+ */
+
+class IOPort {
+  /*! \brief Address in I/O address space
+   *
+   */
+  uint16_t address;
+
+ public:
+  /*! \brief Constructor
+   *  \param addr Address from the I/O address space
+   */
+  explicit constexpr IOPort(uint16_t addr) : address(addr) {}
+
+  /*! \brief Write one byte to the I/O port
+   *  \param val The value to be written
+   */
+  void outb(uint8_t val) const {
+    asm volatile("out %%al, %%dx\n\t" : : "a"(val), "d"(address) :);
+  }
+
+  /*! \brief Write one word (2 bytes) to the I/O port
+   *  \param val The value to be written
+   */
+  void outw(uint16_t val) const {
+    asm volatile("out %%ax, %%dx\n\t" : : "a"(val), "d"(address) :);
+  }
+
+  /*! \brief Read one byte from the I/O port
+   *  \return Read byte
+   */
+  uint8_t inb() const {
+    uint8_t out = 0;
+
+    asm volatile("in %%dx, %%al\n\t" : "=a"(out) : "d"(address) :);
+
+    return out;
+  }
+
+  /*! \brief Read one word (2 bytes) from the I/O port
+   *  \return Read word (2 bytes)
+   */
+  uint16_t inw() const {
+    uint16_t out = 0;
+
+    asm volatile("inw %%dx, %%ax\n\t" : "=a"(out) : "d"(address) :);
+
+    return out;
+  }
+};