can2040: Disable tx state machine before resetting it

It seems that if a single write to the PIO ctrl register both disables and resets a state machine then the PIO may actually execute an instruction. Explicitly disable the state machine in one ctrl register write and then reset the state machine in a subsequent write. Signed-off-by: Kevin O'Connor <[email protected]>
KevinOConnor · Apr 29, 2023 · c4900e1 · c4900e1
1 parent 52450e1
commit c4900e1
Showing 1 changed file with 1 addition and 3 deletions.
diff --git a/src/can2040.c b/src/can2040.c
@@ -247,6 +247,7 @@ static void
 pio_tx_reset(struct can2040 *cd)
 {
     pio_hw_t *pio_hw = cd->pio_hw;
+    pio_hw->ctrl = 0x07 << PIO_CTRL_SM_ENABLE_LSB;
     pio_hw->ctrl = ((0x07 << PIO_CTRL_SM_ENABLE_LSB)
                     | (0x08 << PIO_CTRL_SM_RESTART_LSB));
     pio_hw->irq = (SI_MATCHED | SI_ACKDONE) >> 8; // clear PIO irq flags
@@ -255,9 +256,6 @@ pio_tx_reset(struct can2040 *cd)
     sm->shiftctrl = 0;
     sm->shiftctrl = (PIO_SM0_SHIFTCTRL_FJOIN_TX_BITS
                      | PIO_SM0_SHIFTCTRL_AUTOPULL_BITS);
-    // Must reset again after clearing fifo
-    pio_hw->ctrl = ((0x07 << PIO_CTRL_SM_ENABLE_LSB)
-                    | (0x08 << PIO_CTRL_SM_RESTART_LSB));
 }
 
 // Queue a message for transmission on PIO "tx" state machine