diff options
Diffstat (limited to 'hw/lpc-uart.c')
| -rw-r--r-- | hw/lpc-uart.c | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/hw/lpc-uart.c b/hw/lpc-uart.c index 6995152..3224de9 100644 --- a/hw/lpc-uart.c +++ b/hw/lpc-uart.c @@ -547,6 +547,27 @@ static bool uart_init_hw(unsigned int speed, unsigned int clock) uart_write(REG_LCR, 0x03); /* 8N1 */ uart_write(REG_MCR, 0x03); /* RTS/DTR */ uart_write(REG_FCR, 0x07); /* clear & en. fifos */ + + /* + * On some UART implementations[1], we have observed that characters + * written to the UART during early boot (where no RX path is used, + * so we don't read from RBR) can cause a character timeout interrupt + * once we eventually enable interrupts through the IER. This + * interrupt can only be cleared by reading from RBR (even though we've + * cleared the RX FIFO!). + * + * Unfortunately though, the LCR[DR] bit does *not* indicate that there + * are characters to be read from RBR, so we may never read it, so the + * interrupt continuously fires. + * + * So, manually clear the timeout interrupt by reading the RBR here. + * We discard the read data, but that shouldn't matter as we've just + * reset the FIFO anyway. + * + * 1: seen on the AST2500 SUART. I assume this applies to 2400 too. + */ + uart_read(REG_RBR); + return true; detect_fail: |