diff options
Diffstat (limited to 'chip')
| -rw-r--r-- | chip/lm4/onewire.c | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/chip/lm4/onewire.c b/chip/lm4/onewire.c index 082ce1238a..0c795eeedc 100644 --- a/chip/lm4/onewire.c +++ b/chip/lm4/onewire.c @@ -9,6 +9,7 @@ #include "gpio.h" #include "hooks.h" #include "registers.h" +#include "task.h" #include "timer.h" #define ONEWIRE_PIN (1<<2) /* One-wire pin mask (on GPIO H) */ @@ -56,6 +57,12 @@ static int readbit(void) { int bit; + /* + * The delay between sending the output pulse and reading the bit is + * extremely timing sensitive, so disable interrupts. + */ + interrupt_disable(); + /* Output low */ output0(T_RL); @@ -65,6 +72,13 @@ static int readbit(void) /* Read bit */ bit = readline(); + /* + * Enable interrupt as soon as we've read the bit. The delay to the + * end of the timeslot is a lower bound, so additional latency here is + * harmless. + */ + interrupt_enable(); + /* Delay to end of timeslot */ udelay(T_SLOT - T_MSR); return bit; @@ -75,13 +89,25 @@ static int readbit(void) */ static void writebit(int bit) { + /* + * The delays in the output-low signal for sending 0 and 1 bits are + * extremely timing sensitive, so disable interrupts during that time. + * Interrupts can be enabled again as soon as the output is switched + * back to open-drain, since the delay for the rest of the timeslot is + * a lower bound. + */ if (bit) { + interrupt_disable(); output0(T_W1L); + interrupt_enable(); udelay(T_SLOT - T_W1L); } else { + interrupt_disable(); output0(T_W0L); + interrupt_enable(); udelay(T_SLOT - T_W0L); } + } int onewire_reset(void) |