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lpc176x: Add more filtering to workaround adc hardware defect 

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2019-06-19 16:17:40 -04:00
parent 8d029ad652
commit 8951dc3d51
1 changed files with 11 additions and 1 deletions
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12
src/lpc176x/adc.c
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@ -117,7 +117,8 @@ uint16_t
gpio_adc_read(struct gpio_adc g) gpio_adc_read(struct gpio_adc g)
{ {
adc_status.chan |= ADC_DONE; adc_status.chan |= ADC_DONE;
// Perform median filter on 5 read samples // The lpc176x adc has a defect that causes random reports near
// 0xfff. Work around that with a 5 sample median filter.
uint16_t *p = adc_status.samples; uint16_t *p = adc_status.samples;
uint32_t v0 = p[0], v4 = p[1], v1 = p[2], v3 = p[3], v2 = p[4]; uint32_t v0 = p[0], v4 = p[1], v1 = p[2], v3 = p[3], v2 = p[4];
ORDER(v0, v4); ORDER(v0, v4);
@ -127,6 +128,15 @@ gpio_adc_read(struct gpio_adc g)
ORDER(v1, v3); ORDER(v1, v3);
ORDER(v1, v2); ORDER(v1, v2);
ORDER(v2, v3); ORDER(v2, v3);
if (v3 >= 0xff0 || v4 >= 0xff0) {
ORDER(v0, v1);
if (v2 >= 0xff0)
// At least 3 reports are clearly bogus - return the minimum sample
return v0;
// 1 or 2 bogus reports - return the median of the minimum 3 samples
return v1;
}
// Return the median of the 5 samples
return v2; return v2;
} }