Blackfin: support console-over-JTAG

The Blackfin JTAG has the ability to pass data via a back-channel without
halting the processor.  Utilize that channel to emulate a console.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

common/devices.c

@@ -240,6 +240,9 @@ int devices_init (void)
 #ifdef CONFIG_NETCONSOLE
 	drv_nc_init ();
 #endif
+#ifdef CONFIG_JTAG_CONSOLE
+	drv_jtag_console_init ();
+#endif
 
 	return (0);
 }

cpu/blackfin/Makefile

@@ -17,14 +17,15 @@ EXTRA    :=
 CEXTRA   := initcode.o
 SEXTRA   := start.o
 SOBJS    := interrupt.o cache.o
-COBJS    := cpu.o traps.o interrupts.o reset.o serial.o watchdog.o
+COBJS-y  := cpu.o traps.o interrupts.o reset.o serial.o watchdog.o
+COBJS-$(CONFIG_JTAG_CONSOLE) += jtag-console.o
 
 ifeq ($(CONFIG_BFIN_BOOT_MODE),BFIN_BOOT_BYPASS)
-COBJS    += initcode.o
+COBJS-y  += initcode.o
 endif
 
-SRCS     := $(SEXTRA:.o=.S) $(SOBJS:.o=.S) $(COBJS:.o=.c)
-OBJS     := $(addprefix $(obj),$(COBJS) $(SOBJS))
+SRCS     := $(SEXTRA:.o=.S) $(SOBJS:.o=.S) $(COBJS-y:.o=.c)
+OBJS     := $(addprefix $(obj),$(COBJS-y) $(SOBJS))
 EXTRA    := $(addprefix $(obj),$(EXTRA))
 CEXTRA   := $(addprefix $(obj),$(CEXTRA))
 SEXTRA   := $(addprefix $(obj),$(SEXTRA))

cpu/blackfin/jtag-console.c

+/*
+ * jtag-console.c - console driver over Blackfin JTAG
+ *
+ * Copyright (c) 2008 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2 or later.
+ */
+
+#include <common.h>
+#include <devices.h>
+#include <asm/blackfin.h>
+
+#ifndef CONFIG_JTAG_CONSOLE_TIMEOUT
+# define CONFIG_JTAG_CONSOLE_TIMEOUT 100
+#endif
+
+/* The Blackfin tends to be much much faster than the JTAG hardware. */
+static void jtag_write_emudat(uint32_t emudat)
+{
+	static bool overflowed = false;
+	ulong timeout = get_timer(0) + CONFIG_JTAG_CONSOLE_TIMEOUT;
+	while (bfin_read_DBGSTAT() & 0x1) {
+		if (overflowed)
+			return;
+		if (timeout < get_timer(0))
+			overflowed = true;
+	}
+	overflowed = false;
+	__asm__ __volatile__("emudat = %0;" : : "d"(emudat));
+}
+/* Transmit a buffer.  The format is:
+ * [32bit length][actual data]
+ */
+static void jtag_send(const char *c, uint32_t len)
+{
+	uint32_t i;
+
+	if (len == 0)
+		return;
+
+	/* First send the length */
+	jtag_write_emudat(len);
+
+	/* Then send the data */
+	for (i = 0; i < len; i += 4)
+		jtag_write_emudat((c[i] << 0) | (c[i+1] << 8) | (c[i+2] << 16) | (c[i+3] << 24));
+}
+static void jtag_putc(const char c)
+{
+	jtag_send(&c, 1);
+}
+static void jtag_puts(const char *s)
+{
+	jtag_send(s, strlen(s));
+}
+
+static int jtag_tstc(void)
+{
+	return (bfin_read_DBGSTAT() & 0x2);
+}
+
+/* Receive a buffer.  The format is:
+ * [32bit length][actual data]
+ */
+static size_t inbound_len;
+static int leftovers_len;
+static uint32_t leftovers;
+static int jtag_getc(void)
+{
+	int ret;
+	uint32_t emudat;
+
+	/* see if any data is left over */
+	if (leftovers_len) {
+		--leftovers_len;
+		ret = leftovers & 0xff;
+		leftovers >>= 8;
+		return ret;
+	}
+
+	/* wait for new data ! */
+	while (!jtag_tstc())
+		continue;
+	__asm__("%0 = emudat;" : "=d"(emudat));
+
+	if (inbound_len == 0) {
+		/* grab the length */
+		inbound_len = emudat;
+	} else {
+		/* store the bytes */
+		leftovers_len = min(4, inbound_len);
+		inbound_len -= leftovers_len;
+		leftovers = emudat;
+	}
+
+	return jtag_getc();
+}
+
+int drv_jtag_console_init(void)
+{
+	device_t dev;
+	int ret;
+
+	memset(&dev, 0x00, sizeof(dev));
+	strcpy(dev.name, "jtag");
+	dev.flags = DEV_FLAGS_OUTPUT | DEV_FLAGS_INPUT | DEV_FLAGS_SYSTEM;
+	dev.putc = jtag_putc;
+	dev.puts = jtag_puts;
+	dev.tstc = jtag_tstc;
+	dev.getc = jtag_getc;
+
+	ret = device_register(&dev);
+	return (ret == 0 ? 1 : ret);
+}
+
+#ifdef CONFIG_UART_CONSOLE_IS_JTAG
+/* Since the JTAG is always available (at power on), allow it to fake a UART */
+void serial_set_baud(uint32_t baud) {}
+void serial_setbrg(void)            {}
+int serial_init(void)               { return 0; }
+void serial_putc(const char c)      __attribute__((alias("jtag_putc")));
+void serial_puts(const char *s)     __attribute__((alias("jtag_puts")));
+int serial_tstc(void)               __attribute__((alias("jtag_tstc")));
+int serial_getc(void)               __attribute__((alias("jtag_getc")));
+#endif

include/devices.h

@@ -116,5 +116,8 @@ int	drv_usbtty_init (void);
 #ifdef CONFIG_NETCONSOLE
 int	drv_nc_init (void);
 #endif
+#ifdef CONFIG_JTAG_CONSOLE
+int drv_jtag_console_init (void);
+#endif
 
 #endif	/* _DEVICES_H_ */