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max3421: prevent USB host hang at startup

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On some boards the MAX3421E doesn't report its oscillator ready after a
soft reset (CHIPRES), so hcd_init() waits on USBIRQ_OSCOK forever and the
host hangs at startup before any USB device can be used. Bound the wait so
it proceeds after a timeout; it is a no-op where OSCOK arrives normally.

Needed on the Adafruit Feather ESP32 V2 (classic ESP32) + USB Host
FeatherWing, which otherwise hangs on essentially every cold boot.

Relates to adafruit/circuitpython#10053.
This commit is contained in:
Mikey Sklar
2026-06-30 10:06:38 -07:00
committed by hathach
parent dae3f9a366
commit f96757a19a
1 changed files with 8 additions and 1 deletions
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9
src/portable/analog/max3421/hcd_max3421.c
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@ -504,8 +504,15 @@ bool hcd_init(uint8_t rhport, const tusb_rhport_init_t* rh_init) {
// reset
reg_write(rhport, USBCTL_ADDR, USBCTL_CHIPRES, false);
reg_write(rhport, USBCTL_ADDR, 0, false);
// Bound the oscillator-OK wait. On boards where the MAX3421E is only
// soft-reset (CHIPRES) rather than hardware-reset via nRST, OSCOK may never
// latch, which would otherwise hang the host forever (adafruit/circuitpython#10053).
// The oscillator is generally running regardless, so proceed after a timeout.
uint32_t oscok_retries = 200000;
while( !(reg_read(rhport, USBIRQ_ADDR, false) & USBIRQ_OSCOK_IRQ) ) {
// wait for oscillator to stabilize
if (--oscok_retries == 0) {
break;
}
}
// Mode: Host and DP/DM pull down