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fix USB-PD implementation #936

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Merged
cnlohr merged 2 commits into from
Jul 27, 2026
+15 −1
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fix USB-PD implementation #936

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15e6fd8
fix USB-PD implementation
NyxCode Jul 25, 2026
c215251
move barrier
NyxCode Jul 25, 2026
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16 changes: 15 additions & 1 deletion examples_x035/usbpd_sink/usbpd.h
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Original file line number Diff line number Diff line change
Expand Up @@ -553,7 +553,7 @@ typedef struct
USBPD_CC_e lastCCLine;
USBPD_SPR_CapabilitiesMessage_t caps;
uint8_t messageID;
uint8_t pdoCount;
volatile uint8_t pdoCount;
bool gotSourceGoodCRC;
} USBPD_Instance_t;

Expand Down Expand Up @@ -641,6 +641,11 @@ USBPD_Result_e USBPD_SinkNegotiate( void )
break;

case eSTATE_SOURCE_CAP:
// Wait for the GoodCRC TX (started inside ParsePacket) to finish before
// sending the Request. Without this, SelectPDO's SendMessage races with
// the in-progress GoodCRC transmission (~450 µs at 300 kHz BMC), causing
// strict chargers to reject or ignore the request.
while ( USBPD->CONTROL & PD_TX_EN );
USBPD_SelectPDO( 0, 0 ); // Select the first PDO by default
s_instance.state = eSTATE_WAIT_ACCEPT;
break;
Expand Down Expand Up @@ -770,6 +775,12 @@ USBPD_Result_e USBPD_SelectPDO( uint8_t index, uint32_t voltageIn100mV )
*/
size_t USBPD_GetCapabilities( USBPD_SPR_CapabilitiesMessage_t **capabilities )
{
// Barrier: caps is written by the IRQ via memcpy; without this, LTO can
// prove the main-thread call chain never writes caps and fold all reads to
// zero. The barrier is placed here so every caller gets correct data
// regardless of which state the negotiation exited through.
__asm volatile( "" ::: "memory" );

Comment on lines +782 to +783

@NyxCode NyxCode Jul 25, 2026 •
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Without the barrier (and the volatile field above), negotiation always failed when compiled with LTO

@cnlohr cnlohr Jul 27, 2026

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Got it.

if ( s_instance.pdoCount == 0 )
{
return 0;
Expand Down Expand Up @@ -872,6 +883,8 @@ static void ParsePacket( void )

case eUSBPD_CTRL_MSG_PS_RDY: nextState = eSTATE_PS_RDY; break;

case eUSBPD_CTRL_MSG_WAIT: nextState = eSTATE_CABLE_DETECT; break;

Comment on lines +886 to +887

@NyxCode NyxCode Jul 25, 2026

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The ThinkPad power brick sent the WAIT command, and only negotiated successfully with this

@cnlohr cnlohr Jul 27, 2026

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Got it.

default: break;
}
}
Expand Down Expand Up @@ -931,6 +944,7 @@ void USBPD_IRQHandler( void )
if ( USBPD->STATUS & IF_RX_RESET )
{
USBPD->STATUS |= IF_RX_RESET;
SwitchRXMode();
}
}

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