UART: Fixed UDRC/E behaviour

The interrupt is suposed to fire as soon as it is
enabled is the UDR is empty.

Signed-off-by: Michel Pollet <buserror@gmail.com>

diff --git a/simavr/sim/avr_uart.c b/simavr/sim/avr_uart.c
index 3a7c6ae..14f7bdb 100644 (file)
--- a/simavr/sim/avr_uart.c
+++ b/simavr/sim/avr_uart.c
@@ -140,12 +140,27 @@ static void avr_uart_write(struct avr_t * avr, avr_io_addr_t addr, uint8_t v, vo
                // tell other modules we are "outputing" a byte
                if (avr_regbit_get(avr, p->txen))
                        avr_raise_irq(p->io.irq + UART_IRQ_OUTPUT, v);
-       } else {
+       }
+       if (addr == p->udrc.enable.reg) {
+               /*
+                * If enabling the UDRC interupt, raise it immediately if FIFO is empty
+                */
+               uint8_t udrce = avr_regbit_get(avr, p->udrc.enable);
+               avr_core_watch_write(avr, addr, v);
+               uint8_t nudrce = avr_regbit_get(avr, p->udrc.enable);
+               if (!udrce && nudrce) {
+                       // if the FIDO is not empty (clear timer is flying) we dont
+                       // need to raise the interupt, it will happend when the timer
+                       // is fired.
+                       if (avr_cycle_timer_status(avr, avr_uart_txc_raise, p) == 0)
+                               avr_raise_interrupt(avr, &p->udrc);
+               }
+       }
+       if (addr == p->udrc.raised.reg) {
                // get the bits before the write
                uint8_t udre = avr_regbit_get(avr, p->udrc.raised);
                uint8_t txc = avr_regbit_get(avr, p->txc.raised);
 
-               avr_core_watch_write(avr, addr, v);
 
                avr_clear_interupt_if(avr, &p->udrc, udre);
                avr_clear_interupt_if(avr, &p->txc, txc);
@@ -230,6 +245,7 @@ void avr_uart_init(avr_t * avr, avr_uart_t * p)
        avr_io_setirqs(&p->io, AVR_IOCTL_UART_GETIRQ(p->name), UART_IRQ_COUNT, NULL);
 
        avr_register_io_write(avr, p->r_udr, avr_uart_write, p);
+       avr_register_io_write(avr, p->udrc.enable.reg, avr_uart_write, p);
        avr_register_io_read(avr, p->r_udr, avr_uart_read, p);
        // monitor code that reads the rxc flag, and delay it a bit
        avr_register_io_read(avr, p->rxc.raised.reg, avr_uart_rxc_read, p);