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dcd_msp430x5xx: Improve comments regarding SETUP packet handling.

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This commit is contained in:
William D. Jones 2019-10-29 14:08:39 -04:00
parent 3f0f7cfd07
commit 5d585c03bd
1 changed files with 25 additions and 10 deletions
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35
src/portable/ti/msp430x5xx/dcd_msp430x5xx.c
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@ -515,12 +515,9 @@ static void handle_setup_packet(void)
_setup_packet[i] = setup_buf[i];
}
// 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.
// Clearing SETUPIFG by reading USBVECINT does not set NAK, so now that we
// have a SETUP packet, force NAKs until tinyusb can handle the SETUP
// packet and prepare for a new xfer.
USBIEPCNT_0 |= NAK;
USBOEPCNT_0 |= NAK;
dcd_event_setup_received(0, (uint8_t*) &_setup_packet[0], true);
@ -547,13 +544,31 @@ void __attribute__ ((interrupt(USB_UBM_VECTOR))) USB_UBM_ISR(void)
break;
// 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.
// is received. At this point, even though the hardware is no longer
// forcing NAKs, the EP0 NAK bits should still be set to avoid
// sending/receiving data before tinyusb is ready.
//
// Furthermore, 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
// From my testing, if all of the following hold:
// * OUT EP0 NAK is cleared.
// * IN EP0 NAK is set.
// * DIR bit in USBCTL is clear.
// and an IN packet is received on EP0, the USB core will STALL. Setting
// both EP0 NAKs manually when a SETUP packet is received, as is done
// in handle_setup_packet(), avoids meeting STALL conditions.
//
// TODO: Figure out/explain why the STALL condition can be reached in the
// first place. When I first noticed the STALL, the only two places I
// touched the NAK bits were in dcd_edpt_xfer() and to _set_ (sic) them in
// bus_reset(). SETUP packet handling should've been unaffected.
//
// 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.
// possible SETUP packet. We don't do this right now, as there is no
// "Status Phase done" callback the driver can use. However, SETUP packets
// _are_ correctly handled by the USB core without clearing the NAKs.
case USBVECINT_SETUP_PACKET_RECEIVED:
break;