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dcd_msp430x5xx: Clarify hardware STALL behavior and current vs ideal 

behavior of driver in comments.
This commit is contained in:
William D. Jones 2019-10-29 12:52:56 -04:00
parent ffeb61a710
commit 3f0f7cfd07
1 changed files with 15 additions and 5 deletions
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20
src/portable/ti/msp430x5xx/dcd_msp430x5xx.c
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@ -515,9 +515,12 @@ static void handle_setup_packet(void)
_setup_packet[i] = setup_buf[i];
}
// The NAK bits must be clear to receive a SETUP packet. Clearing SETUPIFG
// by reading USBVECINT does not set NAK, so now that we have a SETUP packet
// force NAKs.
// The EP0 NAK bits must be clear to receive a SETUP packet, according to the
// manual (we don't do this right now- see below comments).
// Race conditions where the hardware STALLs can occur if the NAK bits aren't
// set for both IN/OUT EP0. Clearing SETUPIFG by reading USBVECINT does not
// set NAK, so now that we have a SETUP packet, force NAKs.
// FIXME: Explain more accurately why the STALL occurs.
USBIEPCNT_0 |= NAK;
USBOEPCNT_0 |= NAK;
dcd_event_setup_received(0, (uint8_t*) &_setup_packet[0], true);
@ -526,7 +529,7 @@ static void handle_setup_packet(void)
void __attribute__ ((interrupt(USB_UBM_VECTOR))) USB_UBM_ISR(void)
{
// Setup is special- reading USBVECINT to handle setup packets is done to
// stop NAKs on EP0.
// stop hardware-generated NAKs on EP0.
uint8_t setup_status = USBIFG & SETUPIFG;
if(setup_status)
@ -543,7 +546,14 @@ void __attribute__ ((interrupt(USB_UBM_VECTOR))) USB_UBM_ISR(void)
dcd_event_bus_signal(0, DCD_EVENT_BUS_RESET, true);
break;
// Clear the NAK on EP 0 after a SETUP packet is received.
// Clear the (hardware-enforced) NAK on EP 0 after a SETUP packet
// is received. The NAK bits for EP0 should still be set because it's
// possible for the hardware to STALL in the middle of a control xfer
// if the EP0 NAK bits aren't set properly.
// See: https://e2e.ti.com/support/microcontrollers/msp430/f/166/t/845259
// FIXME: Per manual, we should be clearing the NAK bits of EP0 after the
// Status Phase of a control xfer is done, in preparation of another
// possible setup packet. No clean way to do this right now.
case USBVECINT_SETUP_PACKET_RECEIVED:
break;