YEAH! I got it running . Thanks spanning for your reactions. Better share this with the community:
It took some digging but (as always) the solution was trivial: I had to enable the FP co-processor. I thought this was done by the "
FMXR FPEXC, r0" instruction, but that was not the whole story. That instruction is for enabling the VFP
after it the whole co-processor has been switched on. This was the piece of the puzzle that was missing. All co-processors can be enabled in the "
Coprocessor access register". Each co-processor has two bits to enable it for SVC and/or user mode. The VFP is co-processor cp10 and cp11. The register can be accessed with "
mcr p15, 0, r0, c1, c0, 2". To wrap it all together, the following C function will enable the VFP:
void ENABLE_VFP (void) {
asm(" mrc p15, 0, r0, c1, c0, 2");
asm(" orr r0, r0, #(0xf << 20)");
asm(" mcr p15, 0, r0, c1, c0, 2");
asm(" mov r0, #0x40000000");
asm(" fmxr fpexc, r0");
}
The first three instructions switch the co-processor on while the last two enable the VFP itself.
Be aware that this will only work if you have a single process using the VFP. I used it for a "
led_flasher" type of program.
Regards,
Tom
P.S. I had to do a lot of trial and error to get the above. Because the LEDs on the board were a bit too simple to get sensible feed back I implemented a simple printf. I thought I might as well share it with you. Remarks: it is completely synchronous; it should only be used for debugging; I needed a delay loop for every character otherwise I would loose characters (it might be due to my host machine so try to take it out if you want to); I used some code I found on the web by "Georges Menie", he deserves 99% of the credits . I hope this will help others.
#define UART (0x43f90040)
struct uart
{ volatile unsigned dr; // @0x0
volatile unsigned ecr; // @0x4
volatile unsigned lcrh; // @0x8
volatile unsigned lcrm; // @0x0c
volatile unsigned lcrl; // @0x10
volatile unsigned cr; // @0x14
volatile unsigned fr; // @0x18
volatile unsigned iir; // @0x1C
volatile unsigned ilpr; // @0x20
volatile unsigned ibrd; // @0x24
volatile unsigned fbrd; // @0x28
volatile unsigned lcrh11; // @0x2C
volatile unsigned cr11; // @0x30
};
#define FR_RX_Fifo_Empty 0x10
#define FR_TX_Fifo_Full 0x20
#define FR_RX_Fifo_Full 0x40
#define FR_TX_Fifo_Empty 0x80
struct uart *uart0 = (struct uart*)UART;
#define DELAY (5000)
unsigned int counter;
void toUart(char c) {
while (uart0->fr & FR_TX_Fifo_Full)
;
for (counter = DELAY; counter; counter--);
uart0->dr = (unsigned char) c;
}
char toHex(char c) {
if (c>9) {
return 'a'+(c-10);
} else {
return '0'+c;
}
}
void putchar(char c) {
if (c == '\n') {
toUart('\r');
}
toUart(c);
/*
toUart('(');
toUart('=');
toUart('0');
toUart('x');
toUart(toHex((c>>4)&0x0f));
toUart(toHex( c &0x0f));
toUart(')');
toUart(' ');
*/
}
/*
Copyright 2001, 2002 Georges Menie (www.menie.org)
stdarg version contributed by Christian Ettinger
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
putchar is the only external dependency for this file,
if you have a working putchar, leave it commented out.
If not, uncomment the define below and
replace outbyte(c) by your own function call.
#define putchar(c) outbyte(c)
*/
#include <stdarg.h>
static void printchar(char **str, int c) {
if (str) {
**str = c;
++(*str);
} else {
putchar(c);
}
}
#define PAD_RIGHT 1
#define PAD_ZERO 2
static int prints(char **out, const char *string, int width, int pad)
{
register int pc = 0, padchar = ' ';
if (width > 0) {
register int len = 0;
register const char *ptr;
for (ptr = string; *ptr; ++ptr) ++len;
if (len >= width) width = 0;
else width -= len;
if (pad & PAD_ZERO) padchar = '0';
}
if (!(pad & PAD_RIGHT)) {
for ( ; width > 0; --width) {
printchar (out, padchar);
++pc;
}
}
for ( ; *string ; ++string) {
printchar (out, *string);
++pc;
}
for ( ; width > 0; --width) {
printchar (out, padchar);
++pc;
}
return pc;
}
/* the following should be enough for 32 bit int */
#define PRINT_BUF_LEN 12
static int printi(char **out, int i, int b, int sg, int width, int pad, int letbase)
{
char print_buf[PRINT_BUF_LEN];
register char *s;
register int t, neg = 0, pc = 0;
register unsigned int u = i;
if (i == 0) {
print_buf[0] = '0';
print_buf[1] = '\0';
return prints (out, print_buf, width, pad);
}
if (sg && b == 10 && i < 0) {
neg = 1;
u = -i;
}
s = print_buf + PRINT_BUF_LEN-1;
*s = '\0';
while (u) {
t = u % b;
if( t >= 10 )
t += letbase - '0' - 10;
*--s = t + '0';
u /= b;
}
if (neg) {
if( width && (pad & PAD_ZERO) ) {
printchar (out, '-');
++pc;
--width;
}
else {
*--s = '-';
}
}
return pc + prints (out, s, width, pad);
}
static int print(char **out, const char *format, va_list args )
{
register int width, pad;
register int pc = 0;
char scr[2];
for (; *format != 0; ++format) {
if (*format == '%') {
++format;
width = pad = 0;
if (*format == '\0') break;
if (*format == '%') goto out;
if (*format == '-') {
++format;
pad = PAD_RIGHT;
}
while (*format == '0') {
++format;
pad |= PAD_ZERO;
}
for ( ; *format >= '0' && *format <= '9'; ++format) {
width *= 10;
width += *format - '0';
}
if( *format == 's' ) {
register char *s = (char *)va_arg( args, int );
pc += prints (out, s?s:"(null)", width, pad);
continue;
}
if( *format == 'd' ) {
pc += printi (out, va_arg( args, int ), 10, 1, width, pad, 'a');
continue;
}
if( *format == 'x' ) {
pc += printi (out, va_arg( args, int ), 16, 0, width, pad, 'a');
continue;
}
if( *format == 'X' ) {
pc += printi (out, va_arg( args, int ), 16, 0, width, pad, 'A');
continue;
}
if( *format == 'u' ) {
pc += printi (out, va_arg( args, int ), 10, 0, width, pad, 'a');
continue;
}
if( *format == 'c' ) {
/* char are converted to int then pushed on the stack */
scr[0] = (char)va_arg( args, int );
scr[1] = '\0';
pc += prints (out, scr, width, pad);
continue;
}
}
else {
out:
printchar (out, *format);
++pc;
}
}
if (out) **out = '\0';
va_end( args );
return pc;
}
int printf(const char *format, ...)
{
va_list args;
va_start( args, format );
return print( 0, format, args );
}
int sprintf(char *out, const char *format, ...)
{
va_list args;
va_start( args, format );
return print( &out, format, args );
}
#ifdef TEST_PRINTF
void test() {
char *ptr = "Hello world!";
char *np = 0;
int i = 5;
unsigned int bs = sizeof(int)*8;
int mi;
char buf[80];
mi = (1 << (bs-1)) + 1;
printf("%s\n", ptr);
printf("printf test\n");
printf("%s is null pointer\n", np);
printf("%d = 5\n", i);
printf("%d = - max int\n", mi);
printf("char %c = 'a'\n", 'a');
printf("hex %x = ff\n", 0xff);
printf("hex %02x = 00\n", 0);
printf("signed %d = unsigned %u = hex %x\n", -3, -3, -3);
printf("%d %s(s)%", 0, "message");
printf("\n");
printf("%d %s(s) with %%\n", 0, "message");
sprintf(buf, "justif: \"%-10s\"\n", "left"); printf("%s", buf);
sprintf(buf, "justif: \"%10s\"\n", "right"); printf("%s", buf);
sprintf(buf, " 3: %04d zero padded\n", 3); printf("%s", buf);
sprintf(buf, " 3: %-4d left justif.\n", 3); printf("%s", buf);
sprintf(buf, " 3: %4d right justif.\n", 3); printf("%s", buf);
sprintf(buf, "-3: %04d zero padded\n", -3); printf("%s", buf);
sprintf(buf, "-3: %-4d left justif.\n", -3); printf("%s", buf);
sprintf(buf, "-3: %4d right justif.\n", -3); printf("%s", buf);
}
/*
* if you compile this file with
* gcc -Wall $(YOUR_C_OPTIONS) -DTEST_PRINTF -c printf.c
* you will get a normal warning:
* printf.c:214: warning: spurious trailing `%' in format
* this line is testing an invalid % at the end of the format string.
*
* this should display (on 32bit int machine) :
*
* Hello world!
* printf test
* (null) is null pointer
* 5 = 5
* -2147483647 = - max int
* char a = 'a'
* hex ff = ff
* hex 00 = 00
* signed -3 = unsigned 4294967293 = hex fffffffd
* 0 message(s)
* 0 message(s) with %
* justif: "left "
* justif: " right"
* 3: 0003 zero padded
* 3: 3 left justif.
* 3: 3 right justif.
* -3: -003 zero padded
* -3: -3 left justif.
* -3: -3 right justif.
*/
#endif