Changeset ec16831 in mainline

Timestamp:

2021-08-04T18:52:58Z (3 years ago)

Author:

Marek Benc <dusxmt@…>

Parents:

a977e37

git-author:

Marek Benc <dusxmt@…> (2021-06-23 20:56:38)

git-committer:

Marek Benc <dusxmt@…> (2021-08-04 18:52:58)

Message:

Configure NS16550 transmission format settings on initialization on PCs.

Currently, the NS116550 serial line controller is left with its
settings as it was left by the boot firmware and/or bootloader.
On my computer, this was an invalid configuration, and it left me
with a really slow booting system, since each output character
had to go through the full timeout loop in ns16550_sendb().

This patch adds the necessary bit and register descriptions to configure
the baud rate and transmission settings, as well as configuring them on
post-SMP initialization on ia32 and amd64, currently with values matching
the ns8250 userspace character device driver (38400 baud, 8-bit words,
2 stop bits, no parity).

This could perhaps be changed to be adjustable with a kernel command-line
argument, or through the configuration system.

This change does not affect emulators, since those largely ignore these
settings.

Location:

kernel

Files:

• arch/amd64/src/amd64.c (modified) (1 diff)
• arch/ia32/src/ia32.c (modified) (1 diff)
• genarch/include/genarch/drivers/ns16550/ns16550.h (modified) (3 diffs)
• genarch/src/drivers/ns16550/ns16550.c (modified) (1 diff)

kernel/arch/amd64/src/amd64.c

@@ -224 +224 @@
             ns16550_out_ptr);
         if (ns16550_instance) {
+                ns16550_format_set(ns16550_instance, 38400,
+                    LCR_PARITY_NONE | LCR_STOP_BIT_TWO | LCR_WORD_LEN_8);
 #ifdef CONFIG_NS16550
                 srln_instance_t *srln_instance = srln_init();

kernel/arch/ia32/src/ia32.c

@@ -209 +209 @@
             ns16550_out_ptr);
         if (ns16550_instance) {
+                ns16550_format_set(ns16550_instance, 38400,
+                    LCR_PARITY_NONE | LCR_STOP_BIT_TWO | LCR_WORD_LEN_8);
 #ifdef CONFIG_NS16550
                 srln_instance_t *srln_instance = srln_init();

kernel/genarch/include/genarch/drivers/ns16550/ns16550.h

@@ -43 +43 @@
 #include <console/chardev.h>
 
-#define IER_ERBFI  0x01  /** Enable Receive Buffer Full Interrupt. */
+#define NS156440_CLOCK    115200 /** Internal clock speed, max. baud rate. */
 
-#define LCR_DLAB   0x80  /** Divisor Latch Access bit. */
+#define IER_ERBFI         0x01   /** Enable Receive Buffer Full Interrupt. */
+#define MCR_OUT2          0x08   /** OUT2. */
 
-#define MCR_OUT2   0x08  /** OUT2. */
+#define LCR_DLAB          0x80   /** Divisor Latch Access bit. */
+#define LCR_SBE           0x40   /** RS-232 Break Signal bit. */
+
+#define LCR_PARITY_NONE   0x00   /** No parity bit. */
+#define LCR_PARITY_ODD    0x08   /** Odd parity. */
+#define LCR_PARITY_EVEN   0x18   /** Even parity. */
+#define LCR_PARITY_MARK   0x28   /** Parity bit always one. */
+#define LCR_PARITY_SPACE  0x38   /** Parity bit always zero. */
+
+#define LCR_STOP_BIT_ONE  0x00   /** One stop bit. */
+#define LCR_STOP_BIT_TWO  0x04   /** Two stop bits. */
+
+#define LCR_WORD_LEN_5    0x00   /** 5-bit word length. */
+#define LCR_WORD_LEN_6    0x01   /** 6-bit word length. */
+#define LCR_WORD_LEN_7    0x02   /** 7-bit word length. */
+#define LCR_WORD_LEN_8    0x03   /** 8-bit word length. */
 
 /** NS16550 registers. */
@@ -53 +69 @@
         NS16550_REG_RBR = 0,  /**< Receiver Buffer Register (read). */
         NS16550_REG_THR = 0,  /**< Transmitter Holder Register (write). */
+        NS16550_REG_DLL = 0,  /**< Baud rate divisor latch low byte (write). */
         NS16550_REG_IER = 1,  /**< Interrupt Enable Register. */
+        NS16550_REG_DLH = 1,  /**< Baud rate divisor latch high byte (write). */
         NS16550_REG_IIR = 2,  /**< Interrupt Ident Register (read). */
         NS16550_REG_FCR = 2,  /**< FIFO control register (write). */
@@ -73 +91 @@
 extern ns16550_instance_t *ns16550_init(ioport8_t *, unsigned, inr_t, cir_t,
     void *, outdev_t **);
+extern void ns16550_format_set(ns16550_instance_t *, unsigned, uint8_t);
 extern void ns16550_wire(ns16550_instance_t *, indev_t *);
 

kernel/genarch/src/drivers/ns16550/ns16550.c

@@ -132 +132 @@
 };
 
+/** Configure ns16550 transmission format.
+ *
+ * @param instance   NS 16550 driver instance.
+ * @param baud_rate  Transmission speed in bits per second, also known as baud,
+ *                   maximum value is 115200.
+ * @param lcr_format Line Control Register configuration bits, as defined by
+ *                   the @c LCR_ macros.  These configure the word width,
+ *                   parity type, and stop bit count.
+ */
+void ns16550_format_set(ns16550_instance_t *instance,
+    unsigned baud_rate, uint8_t lcr_format)
+{
+        uint16_t divisor;
+
+        divisor = (uint16_t)(NS156440_CLOCK / baud_rate);
+        if (divisor == 0)
+                divisor = 1;  /* Avoid division by zero. */
+
+        ns16550_reg_write(instance, NS16550_REG_LCR, LCR_DLAB);
+        ns16550_reg_write(instance, NS16550_REG_DLL, divisor & 0xFF);
+        ns16550_reg_write(instance, NS16550_REG_DLH, (divisor >> 8) & 0xFF);
+        ns16550_reg_write(instance, NS16550_REG_LCR, lcr_format & ~LCR_DLAB);
+}
+
 /** Initialize ns16550.
  *