new folder 'avr' with test project to test the AVR on USB-AVR-CPLD

* makefile with compile, program & clean targets
* src/avrtest.c file with test code (@ the moment a simple uart loop)

avr/makefile

@@ -0,0 +1,24 @@
+#AVR-GCC Makefile
+PROJECT = avrtest
+SOURCES = src/avrtest.c
+CC = avr-gcc
+OBJCOPY = avr-objcopy
+MMCU = atmega88
+
+DUMMY_BINARY:=$(shell mkdir -p binary)
+
+CFLAGS = -mmcu=$(MMCU) -Wall -Os -std=gnu99
+
+compile : binary/$(PROJECT).out
+
+binary/$(PROJECT).hex: binary/$(PROJECT).out
+	$(OBJCOPY) -j .text -O ihex binary/$(PROJECT).out binary/$(PROJECT).hex
+
+binary/$(PROJECT).out: $(SOURCES)
+	$(CC) $(CFLAGS) -I./ -o binary/$(PROJECT).out $(SOURCES)
+
+program: binary/$(PROJECT).hex
+	avrdude -p m88 -c buspirate -P /dev/cu.PL2303-003012FA -e -U flash:w:binary/$(PROJECT).hex
+
+clean:
+	rm -rf binary/

avr/src/avrtest.c

@@ -0,0 +1,85 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdint.h>
+
+#ifndef F_CPU
+  #warning "F_CPU wasn't set in makefile, so we do it now with 8.0 MHz"
+  #define F_CPU 1000000UL
+#endif
+
+
+// setting baud rate
+#define BAUD 4800UL
+
+// uart baud rate checks
+#define UBRR_VAL ((F_CPU+BAUD*8)/(BAUD*16)-1)
+#define BAUD_REAL (F_CPU/(16*(UBRR_VAL+1)))
+#define BAUD_ERROR ((BAUD_REAL*1000)/BAUD)
+
+#if ((BAUD_ERROR<990) || (BAUD_ERROR>1010))
+  #error baudrate error higher than 1%! 
+#endif
+
+
+static void uart_init (void);
+static void uart_putc (unsigned char c);
+
+volatile uint8_t got_char;
+volatile unsigned char rx_char;
+
+int main (void)
+{
+
+  // uart rx initialisation
+  uart_init();
+
+  // activate global interrupts
+  sei();
+
+  while(1)
+  {
+    if(got_char) {
+      UCSR0B &= ~(1<<RXCIE0);
+      uart_putc(rx_char);
+      got_char = 0;
+      UCSR0B |= (1<<RXCIE0);
+    }
+  }
+
+  return 0;
+
+}
+
+
+// function to init uart
+static void uart_init (void) {
+  // set baudrate registers (high byte first!)
+  UBRR0H = UBRR_VAL >> 8;
+  UBRR0L = UBRR_VAL & 0xFF;
+  // tx  enable
+  UCSR0B |= (1<<TXEN0) | (1<<RXEN0) | (1<<RXCIE0);
+  // frame format: async mode, no parity, 1 stop bit, 8 bit size
+  UCSR0C |= (3<<UCSZ00);	
+}
+
+
+// send a byte on uart
+static void uart_putc (unsigned char c) {
+  while (!(UCSR0A & (1<<UDRE0))) {}
+  UDR0 = c;
+}
+
+
+ISR(USART_RX_vect) {
+  uint8_t rx_error = 0;
+  //check for frame error
+  if (UCSR0A & (1<<FE0)) {
+    rx_error = 1;
+  }
+  // save rx buffer
+  rx_char = UDR0;
+  // signalise the new rx char if no frame error occured
+  if (!rx_error) {
+    got_char = 1;
+  }
+}