Fast CPU mode approximate serial port transmit throttling to selected baud rate

diff --git a/od-win32/serial_win32.cpp b/od-win32/serial_win32.cpp
index a0e3ff05bc857fde8c35602ab1c24f1dc3fb8626..08c2d133995905aa2cf2bbe09fcaaf2920f2b57b 100644 (file)
--- a/od-win32/serial_win32.cpp
+++ b/od-win32/serial_win32.cpp
@@ -35,6 +35,7 @@
 #define SERIAL_HSYNC_BEFORE_OVERFLOW 200
 #define SERIAL_BREAK_DELAY (20 * maxvpos)
 #define SERIAL_BREAK_TRANSMIT_DELAY 4
+#define MAX_SERIAL_TRANSMIT_PENDING 20
 
 #define SERIAL_MAP
 
@@ -198,6 +199,7 @@ static int dtr;
 static int serial_period_hsyncs;
 static int serial_period_transmit_ccks, serial_period_receive_ccks;
 static int serial_period_transmit_cck_counter, serial_period_receive_cck_counter;
+static bool serial_period_transmit_cck_delayed_irq;
 static int ninebit;
 static int lastbitcycle_active_hsyncs;
 static bool gotlogwrite;
@@ -256,7 +258,7 @@ void SERPER (uae_u16 w)
        }
        mbaud = baud;
 
-       serial_period_transmit_ccks = ((serper & 0x7fff) + 1) * (1 + 8 + ninebit + 1 - 1);
+       serial_period_transmit_ccks = ((serper & 0x7fff) + 1) * (1 + (8 + ninebit) + 1);
        serial_period_receive_ccks = serial_period_transmit_ccks / 4;
 
 #if SERIALLOGGING > 0
@@ -688,7 +690,6 @@ end:
 
 static bool checkshiftempty(void)
 {
-       writeser_flush();
        checksend();
        if (data_in_sershift == 3) {
                data_in_sershift = 0;
@@ -760,7 +761,12 @@ static void serdatcopy(void)
        }
 
        if (data_in_sershift == 0) {
-               INTREQ_INT(0, 1);
+               // delay transmit interrupt if number of queued transmitted bytes is too large.
+               if (!ser_accurate && serial_period_transmit_cck_counter >= MAX_SERIAL_TRANSMIT_PENDING * serial_period_transmit_ccks) {
+                       serial_period_transmit_cck_delayed_irq = true;
+               } else {
+                       INTREQ_INT(0, 1);
+               }
        }
        data_in_sershift = 1;
 
@@ -917,11 +923,13 @@ void serial_hsynchandler (void)
                serdatr_last_got++;
        }
        if (!ser_accurate) {
-               serial_period_transmit_cck_counter += maxhpos;
-               if (serial_period_transmit_cck_counter >= serial_period_transmit_ccks && serial_period_transmit_ccks) {
-                       serial_period_transmit_cck_counter %= serial_period_transmit_ccks;
-                       serial_period_transmit_cck_counter += maxhpos - 1;
-                       checkshiftempty();
+               serial_period_transmit_cck_counter -= maxhpos;
+               if (serial_period_transmit_cck_delayed_irq && serial_period_transmit_cck_counter < MAX_SERIAL_TRANSMIT_PENDING * serial_period_transmit_ccks) {
+                       serial_period_transmit_cck_delayed_irq = false;
+                       INTREQ_INT(0, 1);
+               }
+               if (serial_period_transmit_cck_counter < 0) {
+                       serial_period_transmit_cck_counter = 0;
                }
        } else {
                serial_period_transmit_cck_counter = 0;
@@ -967,6 +975,8 @@ static void flushqueue(void)
 static void SERDAT_send(uae_u32 v)
 {
        uae_u16 w = (uae_u16)v;
+
+       serial_period_transmit_cck_counter += serial_period_transmit_ccks;
 #if SERIALDEBUG > 2
        write_log(_T("SERIAL: SERDAT write 0x%04x (%c) PC=%x\n"), w, dochar(w), M68K_GETPC);
 #endif
@@ -1007,7 +1017,7 @@ static void SERDAT_send(uae_u32 v)
 uae_u16 SERDATR(void)
 {
        serdatr &= 0x03ff;
-       if (!data_in_serdat && (!ser_accurate || (ser_accurate && get_cycles() >= data_in_serdat_delay))) {
+       if (!data_in_serdat && ((!ser_accurate && !serial_period_transmit_cck_delayed_irq) || (ser_accurate && get_cycles() >= data_in_serdat_delay))) {
                serdatr |= 0x2000; // TBE (Transmit buffer empty)
        }
        if (!data_in_sershift && (serdatr & 0x2000)) {