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Resolve/unlatch a latched comparator

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This commit is contained in:
Allen Hill
2026-06-18 19:36:19 -07:00
parent aefd539715
commit 8350f1d426
1 changed files with 23 additions and 7 deletions
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src/avclandrv.c
+23 -7
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@@ -318,11 +318,13 @@ static constexpr uint16_t rtc_status_per =
(uint16_t)(32768UL * 1000UL / RTC_STATUS_PERIOD_MS) - 1U; (uint16_t)(32768UL * 1000UL / RTC_STATUS_PERIOD_MS) - 1U;
void AVCLAN_init() { void AVCLAN_init() {
// Pull-ups are disabled by default
// Set pin 6 and 7 as input // Set pin 6 and 7 as input
PORTA.DIRCLR = (PIN6_bm | PIN7_bm); PORTA.DIRCLR = (PIN6_bm | PIN7_bm);
PORTA.PIN6CTRL = PORT_ISC_INPUT_DISABLE_gc; // Disable input buffer; // Disable input buffer; recommended when using AC
PORTA.PIN7CTRL = PORT_ISC_INPUT_DISABLE_gc; // recommended when using AC PORTA.PIN6CTRL = PORT_ISC_INPUT_DISABLE_gc;
// PA7/AINN1(-) additionally gets a pull-up to help prevent the comparator
// latching high (ie false "driven" bus)
PORTA.PIN7CTRL = PORT_PULLUPEN_bm | PORT_ISC_INPUT_DISABLE_gc;
// Analog comparator config // Analog comparator config
AC2.CTRLA = AC_OUTEN_bm | AC_HYSMODE_25mV_gc | AC_ENABLE_bm; AC2.CTRLA = AC_OUTEN_bm | AC_HYSMODE_25mV_gc | AC_ENABLE_bm;
@@ -666,6 +668,7 @@ uint8_t AVCLAN_readframe(AVCLAN_frame_t *frame, log_t print) {
BAD_CONTROL_PARITY, BAD_CONTROL_PARITY,
STARTBIT_TOO_SHORT, STARTBIT_TOO_SHORT,
STARTBIT_TOO_LONG, STARTBIT_TOO_LONG,
LATCHED_COMPARATOR,
} errno; } errno;
union { union {
uint8_t val; // BAD_LENGTH_RANGE: the out-of-range length value uint8_t val; // BAD_LENGTH_RANGE: the out-of-range length value
@@ -684,11 +687,23 @@ uint8_t AVCLAN_readframe(AVCLAN_frame_t *frame, log_t print) {
while (!BUS_IS_IDLE) { while (!BUS_IS_IDLE) {
startbitlen = TCB1.CNT; startbitlen = TCB1.CNT;
if (startbitlen > (uint16_t)AVCLAN_STARTBIT_LOGIC_0 * 1.2) { if (startbitlen > (uint16_t)AVCLAN_STARTBIT_LOGIC_0 * 1.2) {
// hang until bus is idle to avoid repeated STARTBIT_TOO_LONG
// errors when the AC is stuck (observed when cycling car power and
// mockingboard is externally powered by serial/updi)
while (!BUS_IS_IDLE) {}
err.errno = STARTBIT_TOO_LONG; err.errno = STARTBIT_TOO_LONG;
while (!BUS_IS_IDLE) {
// If bus is "driven" too long, assume the AC2 is latched (e.g.
// because the bus is actually floating). Kick it if so.
// This should prevent/resolve a flood of "STARTBIT_TOO_LONG" errors
if (TCB1.CNT > (uint16_t)(AVCLAN_STARTBIT_LOGIC_0 * 3)) {
err.errno = LATCHED_COMPARATOR;
PORTA.OUTSET = PIN7_bm; // preset high before enabling the driver
PORTA.DIRSET = PIN7_bm; // drive (-) hard high
TCB1.CNT = 0;
while (!BUS_IS_IDLE && TCB1.CNT < (uint16_t)AVCLAN_BIT0_LOGIC_1) {
// Wait a max of ~6μs until bus is idle
}
PORTA.DIRCLR = PIN7_bm; // back to high-Z comparator input
PORTA.OUTCLR = PIN7_bm;
}
}
goto handle_err; goto handle_err;
} }
} }
@@ -797,6 +812,7 @@ uint8_t AVCLAN_readframe(AVCLAN_frame_t *frame, log_t print) {
startEvent(); startEvent();
RS232_Print("ERR(read): "); RS232_Print("ERR(read): ");
switch (err.errno) { switch (err.errno) {
case LATCHED_COMPARATOR: RS232_Print("latched comparator"); break;
case STARTBIT_TOO_SHORT: RS232_Print("start bit too short"); break; case STARTBIT_TOO_SHORT: RS232_Print("start bit too short"); break;
case STARTBIT_TOO_LONG: RS232_Print("start bit too long"); break; case STARTBIT_TOO_LONG: RS232_Print("start bit too long"); break;
case BAD_CONTROLLER_PARITY: case BAD_CONTROLLER_PARITY: