add serial interface and a few std library functions

changes in usart:
  - new functions to setup the serial comunication settings such as baudrate,
    parity and stop bits
  - init function with most common values
  - transmit and receive functions each with a wrapper to send data blocks

changes in libc:
  - new file stdio.c with basic implementation of putch, printf still a prototype
  - new file string.c with memcpy() function

1 files changed, 18 insertions, 0 deletions

diff --git a/sw/z80/kernel/include/pio.h b/sw/z80/kernel/include/pio.h
new file mode 100644
index 0000000..8d72ab0
--- /dev/null
+++ b/sw/z80/kernel/include/pio.h
@@ -0,0 +1,18 @@
+#ifndef __PIO_H__
+#define __PIO_H__
+
+#define PIO_A   0
+#define PIO_B   1
+
+
+void pio_data(int port, uint8_t data);
+void pio_command(int port, uint8_t cmd);
+
+uint8_t pio_read_data(int port);
+
+inline int pio_read_pin(int port, uint8_t pin);
+inline void pio_write_pin(int port, uint8_t pin);
+
+// TODO: implement mode (in/out/both) and interrupt vector
+
+#endif // __PIO_H__