On Fri, Aug 03, 2001 at 02:15:54PM -0700, John D. Davis wrote:
> Does anyone know off hand, the earlies point that I can use printk? I
> added some printk statements to driver/char/console.c and the resulting
> kernel hangs with only the logo showing and no text. Is prom_printf
> something that I should use instead. I put some printk statements in
> tty_io.c and kernel/printk.c and those compiled kernels work.
>
> thanks,
> john davis
>
Like other folks from this list have pointed out, you can use
it as early as the first C line. The output is stored in a memory
buffer and later displayed on your screen when your serial console
is registered.
When porting to a new machine, I often use dev-only patch (i.e.,
not meant to be checked in) to enable seeing printk immediately, *if*
it is a standard UART port. See the attache patch below.
I don't recommand use or implement prom_printf.
Jun
diff -Nru linux/kernel/printk.c.orig linux/kernel/printk.c
--- linux/kernel/printk.c.orig Fri Mar 9 12:34:58 2001
+++ linux/kernel/printk.c Thu Mar 15 14:24:19 2001
@@ -251,6 +251,7 @@
return do_syslog(type, buf, len);
}
+extern void debug_out(char * msg, int len);
asmlinkage int printk(const char *fmt, ...)
{
va_list args;
@@ -296,6 +297,11 @@
break;
}
}
+
+ /* jsun */
+ debug_out(msg, p - msg + line_feed);
+
+ /*
if (msg_level < console_loglevel && console_drivers) {
struct console *c = console_drivers;
while(c) {
@@ -304,6 +310,7 @@
c = c->next;
}
}
+ */
if (line_feed)
msg_level = -1;
}
@@ -494,4 +501,132 @@
if (tty && tty->driver.write)
tty->driver.write(tty, 0, msg, strlen(msg));
return;
+}
+
+
+/* --- CONFIG --- */
+
+/* we need uint32 uint8 */
+/* #include "types.h" */
+typedef unsigned char uint8;
+typedef unsigned int uint32;
+
+/* --- END OF CONFIG --- */
+
+#define UART16550_BAUD_2400 2400
+#define UART16550_BAUD_4800 4800
+#define UART16550_BAUD_9600 9600
+#define UART16550_BAUD_19200 19200
+#define UART16550_BAUD_38400 38400
+#define UART16550_BAUD_57600 57600
+#define UART16550_BAUD_115200 115200
+
+#define UART16550_PARITY_NONE 0
+#define UART16550_PARITY_ODD 0x08
+#define UART16550_PARITY_EVEN 0x18
+#define UART16550_PARITY_MARK 0x28
+#define UART16550_PARITY_SPACE 0x38
+
+#define UART16550_DATA_5BIT 0x0
+#define UART16550_DATA_6BIT 0x1
+#define UART16550_DATA_7BIT 0x2
+#define UART16550_DATA_8BIT 0x3
+
+#define UART16550_STOP_1BIT 0x0
+#define UART16550_STOP_2BIT 0x4
+
+void Uart16550Init(uint32 baud, uint8 data, uint8 parity, uint8 stop);
+
+/* blocking call */
+uint8 Uart16550GetPoll(void);
+
+void Uart16550Put(uint8 byte);
+
+/* ----------------------------------------------------- */
+
+/* === CONFIG === */
+
+#define BASE 0xbfa04200
+#define MAX_BAUD 115200
+#define REG_OFFSET 8
+
+/* === END OF CONFIG === */
+
+/* register offset */
+#define OFS_RCV_BUFFER (0*REG_OFFSET)
+#define OFS_TRANS_HOLD (0*REG_OFFSET)
+#define OFS_SEND_BUFFER (0*REG_OFFSET)
+#define OFS_INTR_ENABLE (1*REG_OFFSET)
+#define OFS_INTR_ID (2*REG_OFFSET)
+#define OFS_DATA_FORMAT (3*REG_OFFSET)
+#define OFS_LINE_CONTROL (3*REG_OFFSET)
+#define OFS_MODEM_CONTROL (4*REG_OFFSET)
+#define OFS_RS232_OUTPUT (4*REG_OFFSET)
+#define OFS_LINE_STATUS (5*REG_OFFSET)
+#define OFS_MODEM_STATUS (6*REG_OFFSET)
+#define OFS_RS232_INPUT (6*REG_OFFSET)
+#define OFS_SCRATCH_PAD (7*REG_OFFSET)
+
+#define OFS_DIVISOR_LSB (0*REG_OFFSET)
+#define OFS_DIVISOR_MSB (1*REG_OFFSET)
+
+
+/* memory-mapped read/write of the port */
+#define UART16550_READ(y) (*((volatile uint8*)(BASE + y)))
+#define UART16550_WRITE(y, z) ((*((volatile uint8*)(BASE + y))) = z)
+
+#define DEBUG_LED (*(unsigned short*)0xb7ffffc0)
+#define OutputLED(x) (DEBUG_LED = x)
+
+void Uart16550Init(uint32 baud, uint8 data, uint8 parity, uint8 stop)
+{
+ /* disable interrupts */
+ UART16550_WRITE(OFS_INTR_ENABLE, 0);
+
+ /* set up buad rate */
+ {
+ uint32 divisor;
+
+ /* set DIAB bit */
+ UART16550_WRITE(OFS_LINE_CONTROL, 0x80);
+
+ /* set divisor */
+ divisor = MAX_BAUD / baud;
+ UART16550_WRITE(OFS_DIVISOR_LSB, divisor & 0xff);
+ UART16550_WRITE(OFS_DIVISOR_MSB, (divisor & 0xff00)>>8);
+
+ /* clear DIAB bit */
+ UART16550_WRITE(OFS_LINE_CONTROL, 0x0);
+ }
+
+ /* set data format */
+ UART16550_WRITE(OFS_DATA_FORMAT, data | parity | stop);
+}
+
+uint8 Uart16550GetPoll(void)
+{
+ while((UART16550_READ(OFS_LINE_STATUS) & 0x1) == 0);
+ return UART16550_READ(OFS_RCV_BUFFER);
+}
+
+
+void Uart16550Put(uint8 byte)
+{
+ while ((UART16550_READ(OFS_LINE_STATUS) &0x20) == 0);
+ UART16550_WRITE(OFS_SEND_BUFFER, byte);
+}
+
+/* ---------------------------------------------------------- */
+
+void debug_out(char * msg, int len)
+{
+ int i;
+ for (i=0; i< len; i++) {
+ if (msg[i] == '\n') {
+ Uart16550Put('\r');
+ Uart16550Put('\n');
+ } else {
+ Uart16550Put(msg[i]);
+ }
+ }
}
