diff options
| author | Richard Braun <rbraun@sceen.net> | 2018-02-22 15:12:51 +0000 |
|---|---|---|
| committer | Peter Maydell <peter.maydell@linaro.org> | 2018-02-22 15:12:51 +0000 |
| commit | f6bfe45af2a9bd1b929955ca3bf54726d1e68d88 (patch) | |
| tree | 192a87b7baeb70244561b22df6442fbda77eebf4 | |
| parent | 1c3db49d39d66646ff546ec26f36e3b9040f3504 (diff) | |
| download | qemu-f6bfe45af2a9bd1b929955ca3bf54726d1e68d88.tar.gz | |
hw/char/stm32f2xx_usart: fix TXE/TC bit handling
I/O currently being synchronous, there is no reason to ever clear the
SR_TXE bit. However the SR_TC bit may be cleared by software writing
to the SR register, so set it on each write.
In addition, fix the reset value of the USART status register.
Signed-off-by: Richard Braun <rbraun@sceen.net>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
[PMM: removed XXX tag from comment, since it isn't something
we need to come back and fix in QEMU]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
| -rw-r--r-- | hw/char/stm32f2xx_usart.c | 12 | ||||
| -rw-r--r-- | include/hw/char/stm32f2xx_usart.h | 7 |
2 files changed, 14 insertions, 5 deletions
diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c index 07b462d4b6..032b5fda13 100644 --- a/hw/char/stm32f2xx_usart.c +++ b/hw/char/stm32f2xx_usart.c @@ -96,12 +96,10 @@ static uint64_t stm32f2xx_usart_read(void *opaque, hwaddr addr, switch (addr) { case USART_SR: retvalue = s->usart_sr; - s->usart_sr &= ~USART_SR_TC; qemu_chr_fe_accept_input(&s->chr); return retvalue; case USART_DR: DB_PRINT("Value: 0x%" PRIx32 ", %c\n", s->usart_dr, (char) s->usart_dr); - s->usart_sr |= USART_SR_TXE; s->usart_sr &= ~USART_SR_RXNE; qemu_chr_fe_accept_input(&s->chr); qemu_set_irq(s->irq, 0); @@ -137,7 +135,9 @@ static void stm32f2xx_usart_write(void *opaque, hwaddr addr, switch (addr) { case USART_SR: if (value <= 0x3FF) { - s->usart_sr = value; + /* I/O being synchronous, TXE is always set. In addition, it may + only be set by hardware, so keep it set here. */ + s->usart_sr = value | USART_SR_TXE; } else { s->usart_sr &= value; } @@ -151,8 +151,12 @@ static void stm32f2xx_usart_write(void *opaque, hwaddr addr, /* XXX this blocks entire thread. Rewrite to use * qemu_chr_fe_write and background I/O callbacks */ qemu_chr_fe_write_all(&s->chr, &ch, 1); + /* XXX I/O are currently synchronous, making it impossible for + software to observe transient states where TXE or TC aren't + set. Unlike TXE however, which is read-only, software may + clear TC by writing 0 to the SR register, so set it again + on each write. */ s->usart_sr |= USART_SR_TC; - s->usart_sr &= ~USART_SR_TXE; } return; case USART_BRR: diff --git a/include/hw/char/stm32f2xx_usart.h b/include/hw/char/stm32f2xx_usart.h index 9d03a7527c..84c4029777 100644 --- a/include/hw/char/stm32f2xx_usart.h +++ b/include/hw/char/stm32f2xx_usart.h @@ -37,7 +37,12 @@ #define USART_CR3 0x14 #define USART_GTPR 0x18 -#define USART_SR_RESET 0x00C00000 +/* + * NB: The reset value mentioned in "24.6.1 Status register" seems bogus. + * Looking at "Table 98 USART register map and reset values", it seems it + * should be 0xc0, and that's how real hardware behaves. + */ +#define USART_SR_RESET (USART_SR_TXE | USART_SR_TC) #define USART_SR_TXE (1 << 7) #define USART_SR_TC (1 << 6) |