servo_micro: Allow setting the baud rate for usart

We set the baud rate in increments of 100 baud, to avoid
overflowing the 16-bit wValue integer (921600 is the highest we
are likely to use).

Also, increment the buffer size for USART3 to 1024 bytes. That
helps a bit to avoid losing characters, but we still can't keep
up if the host is printing at maximum speed.

BRANCH=servo
BUG=chromium:876651
TEST=baud usart2/3/4 115200 in servo_micro console
TEST=dut-control cpu_uart_baudrate:921600
     seq 1 1000 shows numbers 1 to 226 before buffer overflows

Change-Id: Ifca266189f93def493f207dd29d2cceca4d8d68f
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1189782
Reviewed-by: Nick Sanders <nsanders@chromium.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/chip/stm32/usb-stream.h b/chip/stm32/usb-stream.h
index f89d62a65c..af96db551d 100644
--- a/chip/stm32/usb-stream.h
+++ b/chip/stm32/usb-stream.h
@@ -277,6 +277,13 @@ enum usb_usart {
 	USB_USART_REQ_BAUD = 2,
 	USB_USART_SET_BAUD = 3,
 };
+
+/*
+ * baud rate is req/set in multiples of 100, to avoid overflowing
+ * 16-bit integer.
+ */
+#define USB_USART_BAUD_MULTIPLIER 100
+
 int usb_usart_interface(struct usb_stream_config const *config,
 		    struct usart_config const *usart,
 		    int interface, usb_uint *rx_buf, usb_uint *tx_buf);