My initial feeling would be endian but you say you have tested this
with float? The only other thing I can think of is the reversal of the 4 bytes.
As floats are 32 bits on the platform I am assuming the memory access is also 32
bits. A double is normally 64 bits (not sure on the Arm7tdmi) but as the memory
access is 32 bits (again I am making an assumption) it could be that you need to
reverse the first 4 bytes with the last 4.
Again without any first had experience of the platform and without knowing
what is attached at the other end it is a bit of a stab in the dark.
It would load the processor up more but the alternative not to have to
worry about this would be to send the number in Ascii and then convert this back
to a number. Like I say though this will cause more processing and may not be
desirable. This would make the solution platform independent as you would not
have to worry about memory architectures.
Adam
2009/10/7 miles
<address@hidden>
Hi
All,
I am running into an issue where it looks like the tiny2.11
(arm7tdmi) board can store double precision floating point numbers, but does
not perform arithmetic (addition, multiplication) correctly. Has anyone
seen this, and/or resolved this before?
As a test, I have been trying
to send a byte array of length 8 representing a double precision number over
serial (via USB) to the Autopilot, use memcpy to copy that buffer to a
variable of type double, and then do some simple addition, and send the result
back over serial. Below is the Autopilot code I am using. Note
that all of this works as expected for "float" variables, but seems to break
for "double" variables!
#include "std.h"
#include
"init_hw.h"
#include "sys_time.h"
#include "led.h"
#include
"usb_serial.h"
static inline void main_init( void );
static inline
void main_periodic_task( void );
int main( void ) {
main_init();
while(1) {
if
(sys_time_periodic())
main_periodic_task();
}
return 0;
}
static
inline void main_init( void ) {
hw_init();
sys_time_init();
led_init();
VCOM_init();
enableIRQ();
}
static inline void main_periodic_task( void )
{
LED_TOGGLE(1);
unsigned char
buf[8];
unsigned char buf2[8];
double x;
int c =
0;
int c2 = 0;
// read 8 bytes from serial (over
USB)
while (c < 8) {
if
(VCOM_check_available()) {
buf[c] =
VCOM_getchar();
c++;
}
}
// deserialize byte array to
float:
memcpy(&x, buf, 8);
// modify float
x
= x + 1.0;
// serialize float to byte array for sending
memcpy(buf2, &x, 8);
c2 = 0;
while (c2 < 8)
{
VCOM_putchar(buf2[c2]);
c2++;
}
}
--
Miles
Johnson
_______________________________________________
Paparazzi-devel
mailing list
address@hidden
http://lists.nongnu.org/mailman/listinfo/paparazzi-devel