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Change TMP006 temperature calculation to use FP.

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The temperature calculation currently uses fixed point operations.
Change it to use floating point for better readability and maintenance.
Also changes disable_fpu() to accept parameter which serves as
optimization barrier to prevent floating point operations after
disabling FPU.

BUG=chrome-os-partner:7801
TEST=In console, tempremote "tempremote 29715 -105000 6390" gives 28506.

Change-Id: Ib766904b8feb9a78eac9f7cd53afeca85091c5a5
Signed-off-by: Vic Yang <victoryang@chromium.org>
This commit is contained in:
Vic Yang
2012-02-15 15:36:40 -08:00
parent 8236345574
commit 93d77ada6c
3 changed files with 43 additions and 48 deletions
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64
common/temp_sensor.c
View File

@@ -11,6 +11,9 @@
#include "util.h"
#include "console.h"
#include "board.h"
#include "task.h"
#include "fpu.h"
#include "math.h"
/* Defined in board_temp_sensor.c. Must be in the same order as
* in enum temp_sensor_id.
@@ -44,52 +47,39 @@ int temp_sensor_tmp006_read_die_temp(const struct temp_sensor_t* sensor)
* Parameters:
* Tdie: Die temperature in 1/100 K.
* Vobj: Voltage read from register 0. In nV.
* S0: Sensitivity factor in 1/1000.
* S0: Sensitivity factor in 1e-17.
* Return:
* Object temperature in 1/100 K.
*/
int temp_sensor_tmp006_calculate_object_temp(int Tdie, int Vobj, int S0)
int temp_sensor_tmp006_calculate_object_temp(int Tdie_i, int Vobj_i, int S0_i)
{
int32_t Tx, S19, Vos, Vx, fv9, ub, lb;
float Tdie, Vobj, S0;
float Tx, S, Vos, Vx, fv, Tobj, T4;
int Tobj_i;
/* Calculate according to TMP006 users guide.
* Division is delayed when possible to preserve precision, but should
* not cause overflow.
* Assuming Tdie is between 200K and 400K, and S0 between 3e-14 and
* 9e-14, the maximum value during the calculation should be less than
* (1 << 30), which fits in int32_t.
*/
Tx = Tdie - 29815;
/* S19 is the sensitivity multipled by 1e19 */
S19 = S0 * (100000 + 175 * Tx / 100 -
1678 * Tx / 100 * Tx / 100000) / 1000;
/* Vos is the offset voltage in nV */
Vos = -29400 - 570 * Tx / 100 + 463 * Tx / 100 * Tx / 10000;
enable_fpu();
Tdie = (float)Tdie_i * 1e-2f;
Vobj = (float)Vobj_i * 1e-9f;
S0 = (float)S0_i * 1e-17f;
/* Calculate according to TMP006 users guide. */
Tx = Tdie - 298.15f;
/* S is the sensitivity */
S = S0 * (1.0f + 1.75e-3f * Tx - 1.678e-5f * Tx * Tx);
/* Vos is the offset voltage */
Vos = -2.94e-5f - 5.7e-7f * Tx + 4.63e-9f * Tx * Tx;
Vx = Vobj - Vos;
/* fv9 is Seebeck coefficient f(Vobj) multipled by 1e9 */
fv9 = Vx + 134 * Vx / 100000 * Vx / 100000;
/* fv is Seebeck coefficient f(Vobj) */
fv = Vx + 13.4f * Vx * Vx;
/* The last step in the calculation involves square root, so we use
* binary search.
* Assuming the object temperature is between 200K and 400K, the search
* should take at most 14 iterations.
*/
ub = 40000;
lb = 20000;
while (lb != ub) {
int32_t t, rhs, lhs;
T4 = Tdie * Tdie * Tdie * Tdie + fv / S;
Tobj = sqrtf(sqrtf(T4));
Tobj_i = (int32_t)(Tobj * 100.0f);
t = (ub + lb) / 2;
lhs = t / 100 * t / 10000 * t / 10000 * (S19/100) / 1000 * t;
rhs = Tdie / 100 * Tdie / 10000 * Tdie / 10000 * (S19/100) / 1000 *
Tdie + fv9 * 1000;
if (lhs > rhs)
ub = t;
else
lb = t + 1;
}
disable_fpu(Tobj_i);
return ub;
return Tobj_i;
}
int temp_sensor_tmp006_read_object_temp(const struct temp_sensor_t* sensor)

21
core/cortex-m/fpu.c
View File

@@ -10,17 +10,20 @@
void enable_fpu(void)
{
interrupt_disable();
asm("mrs r0, control\n"
"orr r0, r0, #(1 << 2)\n"
"msr control, r0\n"
"isb");
asm volatile("mrs r0, control;"
"orr r0, r0, #(1 << 2);"
"msr control, r0;"
"isb;");
}
void disable_fpu(void)
void disable_fpu(int32_t v)
{
asm("mrs r0, control\n"
"bic r0, r0, #(1 << 2)\n"
"msr control, r0\n"
"isb");
/* Optimization barrier to force compiler generate floating point
* calculation code for 'v' before disabling FPU. */
asm volatile("" : : "r" (v) : "memory");
asm volatile("mrs r0, control;"
"bic r0, r0, #(1 << 2);"
"msr control, r0;"
"isb;");
interrupt_enable();
}

6
include/fpu.h
View File

@@ -11,7 +11,9 @@
/* Enables FPU. Note that this function also disables interrupt. */
void enable_fpu(void);
/* Disables FPU. This function also enables interrupt. */
void disable_fpu(void);
/* Disables FPU. This function also enables interrupt.
* The value passed in serves as optimization barrier. This value would be
* calculated before FPU is disabled regardless of compiler optimization. */
void disable_fpu(int32_t);
#endif /* __EC_FPU_H */