timer: Avoid infinite cycle timer on TCNT write

[simavr] / tests / atmega88_uart_echo.c

diff --git a/tests/atmega88_uart_echo.c b/tests/atmega88_uart_echo.c
index c2b4ba3..31f0ab4 100644 (file)
--- a/tests/atmega88_uart_echo.c
+++ b/tests/atmega88_uart_echo.c
@@ -21,14 +21,28 @@
  */
 #include "avr_mcu_section.h"
 AVR_MCU(F_CPU, "atmega88");
+// tell simavr to listen to commands written in this (unused) register
+AVR_MCU_SIMAVR_COMMAND(&GPIOR0);
 
+/*
+ * This small section tells simavr to generate a VCD trace dump with changes to these
+ * registers.
+ * Opening it with gtkwave will show you the data being pumped out into the data register
+ * UDR0, and the UDRE0 bit being set, then cleared
+ */
+const struct avr_mmcu_vcd_trace_t _mytrace[]  _MMCU_ = {
+       { AVR_MCU_VCD_SYMBOL("UDR0"), .what = (void*)&UDR0, },
+       { AVR_MCU_VCD_SYMBOL("UDRE0"), .mask = (1 << UDRE0), .what = (void*)&UCSR0A, },
+       { AVR_MCU_VCD_SYMBOL("GPIOR1"), .what = (void*)&GPIOR1, },
+};
 
-static int uart_putchar(char c, FILE *stream) {
-  if (c == '\n')
-    uart_putchar('\r', stream);
-  loop_until_bit_is_set(UCSR0A, UDRE0);
-  UDR0 = c;
-  return 0;
+static int uart_putchar(char c, FILE *stream)
+{
+       if (c == '\n')
+               uart_putchar('\r', stream);
+       loop_until_bit_is_set(UCSR0A, UDRE0);
+       UDR0 = c;
+       return 0;
 }
 
 static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL,
@@ -41,6 +55,7 @@ volatile uint8_t done = 0;
 ISR(USART_RX_vect)
 {
        uint8_t b = UDR0;
+       GPIOR1 = b; // for the trace file
        buffer[bindex++] = b;
        buffer[bindex] = 0;
        if (b == '\n')
@@ -49,11 +64,28 @@ ISR(USART_RX_vect)
 
 int main()
 {
+       // this tell simavr to put the UART in loopback mode
+       GPIOR0 = SIMAVR_CMD_UART_LOOPBACK;
+
        stdout = &mystdout;
 
-       // enable receiver
+       UCSR0C |= (3 << UCSZ00); // 8 bits
+       // see http://www.nongnu.org/avr-libc/user-manual/group__util__setbaud.html
+#define BAUD 38400
+#include <util/setbaud.h>
+       UBRR0H = UBRRH_VALUE;
+       UBRR0L = UBRRL_VALUE;
+#if USE_2X
+       UCSR0A |= (1 << U2X0);
+#else
+       UCSR0A &= ~(1 << U2X0);
+#endif
+
+       // enable receiver & transmitter
        UCSR0B |= (1 << RXCIE0) | (1 << RXEN0) | (1 << TXEN0);
 
+       // this tells simavr to start the trace
+       GPIOR0 = SIMAVR_CMD_VCD_START_TRACE;
        sei();
        printf("Hey there, this should be received back\n");