hello.c

00001 /* hello.c -- Simple Hello World for 68HC11 bootstrap mode
00002 Copyright 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
00003 Written by Stephane Carrez (stcarrez@nerim.fr)
00004 
00005 This file is part of GEL.
00006 
00007 GEL is free software; you can redistribute it and/or modify
00008 it under the terms of the GNU General Public License as published by
00009 the Free Software Foundation; either version 2, or (at your option)
00010 any later version.
00011 
00012 GEL is distributed in the hope that it will be useful,
00013 but WITHOUT ANY WARRANTY; without even the implied warranty of
00014 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
00015 GNU General Public License for more details.
00016 
00017 You should have received a copy of the GNU General Public License
00018 along with GEL; see the file COPYING. If not, write to
00019 the Free Software Foundation, 59 Temple Place - Suite 330,
00020 Boston, MA 02111-1307, USA. */
00021 
00073 /* Part 1: 68HC11 Definitions.
00074 
00075 This part defines several flags and values to access the
00076 68HC11 SIO registers. The SIO registers are mapped in memory
00077 and are therefore accessed as a global variable.
00078 
00079 The complete list of flags are available when you include
00080 the following file:
00081 
00082 #include <sys/ports.h>
00083 
00084 They are defined in <asm-m68hc11/ports_def_F.h>,
00085 <asm-m68hc11/ports_def_E.h> or <asm-m68hc12/ports_def.h>
00086 depending on the microcontroller.
00087 
00088 */
00089 #define M6811_BAUD 0x2B /* SCI Baud register */
00090 #define M6811_SCCR1 0x2C /* SCI Control register 1 */
00091 #define M6811_SCCR2 0x2D /* SCI Control register 2 */
00092 #define M6811_SCSR 0x2E /* SCI Status register */
00093 #define M6811_SCDR 0x2F /* SCI Data (Read => RDR, Write => TDR) */
00094 
00095 /* Flags of the SCCR2 register. */
00096 #define M6811_TE 0x08 /* Transmit Enable */
00097 #define M6811_RE 0x04 /* Receive Enable */
00098 
00099 /* Flags of the SCSR register. */
00100 #define M6811_TDRE 0x80 /* Transmit Data Register Empty */
00101 
00102 /* Flags of the BAUD register. */
00103 #define M6811_SCP1 0x20 /* SCI Baud rate prescaler select */
00104 #define M6811_SCP0 0x10
00105 #define M6811_SCR2 0x04 /* SCI Baud rate select */
00106 #define M6811_SCR1 0x02
00107 #define M6811_SCR0 0x01
00108 
00109 #define M6811_BAUD_DIV_1 (0)
00110 #define M6811_BAUD_DIV_3 (M6811_SCP0)
00111 #define M6811_BAUD_DIV_4 (M6811_SCP1)
00112 #define M6811_BAUD_DIV_13 (M6811_SCP1|M6811_SCP0)
00113 
00114 #define M6811_DEF_BAUD M6811_BAUD_DIV_4 /* 1200 baud */
00115 
00116 /* The I/O registers are represented by a volatile array.
00117 Address if fixed at link time. For this particular example,
00118 the _io_ports address is defined in the `memory.x' file. */
00119 extern volatile unsigned char _io_ports[];
00120 
00121 /* Part 2: 68HC11 SIO Operations.
00122 
00123 This part defines some functions to write characters
00124 on the SIO. They access the IO register through the
00125 `io_ports' global variable.
00126 
00127 These operations can be used in a program by using
00128 the following include:
00129 
00130 #include <sys/sio.h>
00131 
00132 */
00144 static inline void
00145 serial_send (char c)
00146 {
00147 /* Wait until the SIO has finished to send the character. */
00148 while (!(_io_ports[M6811_SCSR] & M6811_TDRE))
00149 continue;
00150 
00151 _io_ports[M6811_SCDR] = c;
00152 _io_ports[M6811_SCCR2] |= M6811_TE;
00153 }
00154 
00155 void
00156 serial_print (const char *msg)
00157 {
00158 while (*msg != 0)
00159 serial_send (*msg++);
00160 }
00161 
00162 
00163 /* Part 3: Hello World
00164 
00165 When the function 'main' is entered, the stack pointer is
00166 initialized, the global variables are initialized but the
00167 SIO as well as other 68HC11 devices are not yet initialized.
00168 In this example, we first configure the SIO by setting
00169 the baud rate and the character format. The SIO must then
00170 be started by enabling the transmitter and receiver.
00171 
00172 The SIO initialization is inlined here for clarity but it
00173 is implemented by the 'serial_init' operation available when
00174 <sys/sio.h> is included.
00175 
00176 Once the SIO is initialized, we can write messages using
00177 serial_print().
00178 
00179 Note: In this example, the main() function returns and this will give
00180 back control to the startup code which will in turn call exit(). The
00181 exit() will loop forever arround a 'wai' instruction. Indeed, a real
00182 68HC11 hardware has no way to exit!
00183 */
00184 
00185 int
00186 main ()
00187 {
00188 /* Configure the SCI to send at M6811_DEF_BAUD baud. */
00189 _io_ports[M6811_BAUD] = M6811_DEF_BAUD;
00190 
00191 /* Setup character format 1 start, 8-bits, 1 stop. */
00192 _io_ports[M6811_SCCR1] = 0;
00193 
00194 /* Enable receiver and transmitter. */
00195 _io_ports[M6811_SCCR2] = M6811_TE | M6811_RE;
00196 
00197 serial_print ("Hello world!\n");
00198 return 0;
00199 }