UART FCR register write tracing code (com.c, NetBSD)

--- com.c.orig	2021-01-01 17:50:19.699234954 +0900
+++ com.c	2021-01-11 18:13:47.723157894 +0900
@@ -128,10 +128,12 @@ __KERNEL_RCSID(0, "$NetBSD: com.c,v 1.36

 #include "ioconf.h"

+#if 0
 #define	CSR_WRITE_1(r, o, v)	\
 	bus_space_write_1((r)->cr_iot, (r)->cr_ioh, (r)->cr_map[o], v)
 #define	CSR_READ_1(r, o)	\
 	bus_space_read_1((r)->cr_iot, (r)->cr_ioh, (r)->cr_map[o])
+#endif
 #define	CSR_WRITE_2(r, o, v)	\
 	bus_space_write_2((r)->cr_iot, (r)->cr_ioh, (r)->cr_map[o], v)
 #define	CSR_READ_2(r, o)	\
@@ -274,6 +276,76 @@ static const bus_size_t com_std_map[COM_
 #define COM_BARRIER(r, f) \
 	bus_space_barrier((r)->cr_iot, (r)->cr_ioh, 0, (r)->cr_nports, (f))

+struct event_rec_t {
+	unsigned char reg;
+	unsigned char write;
+	unsigned char dat;
+};
+
+#define MAX_EVENTS	2048
+static struct event_rec_t event_rec[MAX_EVENTS] = {{0,0,0}};
+static int event_index = 0;
+
+static void event_record(int reg, int write, int dat)
+{
+	if (event_index < MAX_EVENTS) {
+		event_rec[event_index].reg = reg;
+		event_rec[event_index].write = write;
+		event_rec[event_index].dat = dat;
+		event_index++;
+	}
+}
+
+static void event_show(void)
+{
+	static const char *string[] = {
+		"COM_REG_RXDATA",
+		"COM_REG_TXDATA",
+		"COM_REG_DLBL",
+		"COM_REG_DLBH",
+		"COM_REG_IER",
+		"COM_REG_IIR",
+		"COM_REG_FIFO",
+		"COM_REG_TCR",
+		"COM_REG_EFR",
+		"COM_REG_TLR",
+		"COM_REG_LCR",
+		"COM_REG_MCR",
+		"COM_REG_LSR",
+		"COM_REG_MSR",
+		"COM_REG_USR",
+		"COM_REG_TFL",
+		"COM_REG_RFL",
+		"COM_REG_HALT",
+		"COM_REG_MDR1",
+	};
+
+	int i;
+	for (i = 0; i < event_index; i++) {
+		printf("%04d %s %s %02x\n", i,
+			string[event_rec[i].reg],
+			event_rec[i].write ? "<-" : "->",
+			event_rec[i].dat);
+	}
+}
+
+static void CSR_WRITE_1(struct com_regs *r, int o, int v)
+{
+//	if (o == COM_REG_FIFO) v = 0;
+	bus_space_write_1(r->cr_iot, r->cr_ioh, r->cr_map[o], v);
+	if (o == COM_REG_FIFO) event_record(o, 1, v);
+}
+
+static uint8_t CSR_READ_1(struct com_regs *r, int o)
+{
+	uint8_t v;
+
+	v = bus_space_read_1(r->cr_iot, r->cr_ioh, r->cr_map[o]);
+	// event_record(o, 0, v);
+
+	return v;
+}
+
 /*
  * com_init_regs --
  *	Driver front-ends use this to initialize our register map
@@ -1307,7 +1379,15 @@ com_break(struct com_softc *sc, int onof
 			sc->sc_tbc = 0;
 			sc->sc_heldchange = 1;
 		} else
+		{
+			printf("%s: iot %p iobase %lx ioh %lx\n",
+				device_xname(sc->sc_dev),
+				sc->sc_regs.cr_iot,
+				sc->sc_regs.cr_iobase,
+				sc->sc_regs.cr_ioh);
+			event_show();
 			com_loadchannelregs(sc);
+		}
 	}
 }