Serial Port(s) (USART) Questions:

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Serial Port(s) (USART) Questions:

(7 posts) (4 voices)

Started 5 years ago by leaflabsandy
Latest reply from poslathian

leaflabsandy
Member

Platform: Windows XP SP3
Device: Maple Rev. 3
Version: 0.5.0

Serial Port(s) (USART) Questions:

#1. What is the receive buffer size for the USARTS?
Is it adjustable?

#2. Does the Tx on the USART have also a buffer size?
Is it also adjustable?

#3. The Arduino serial command "Serialx.flush()" (all three ports) does not work eg compile?

#4. What are the standard fixed baud rates for the serial ports?

Note: On the Arduino they were fixed. In the setup using Serialx.begin(baud); fixed baud error checking was performed. Not on the Maple?

On the Maple, Inserting "any" value for the baud in Serialx.begin(baud); is OK and not checked for?

#5. Is Max. baud rate for USART1 is 4.5 M/bits/sec ~ 450,000 baud?

#6. Is Max. baud rate for USART2 & USART3 is 2.5 M/bits/sec ~ 250,000 baud?

Ref. Standard / Special Baud Rates:

Standard baud rates:
•110 •300 •600 •1200 •2400 •4800 •9600
•14400 •19200 •28800 •38400 •56000
•57600 •115200

Special baud rates:
•128000 •153600 •230400
•256000 •460800 •921600

Posted 5 years ago #
bnewbold
Ex-Leaflabs

#1-2, 64 bytes each in the low level implementation (see ./libmaple/usart.* and ./wirish/comms/HardwareSerial.* in libmaple for more details)

#3: not implemented, noted

#4-6: right now we #define USART_MAX_BAUD 225000 for all devices. For more details on the granularity of specific baudrates check out the STM32 hardware reference guide and see our implementation in ./libmaple/usart.c:usart_init(). I don't see any reason to restrict users to popular baudrates, but perhaps we should have a table of them in the docs to reduce confusion? They do mention 9600 baud as the most common already.

Posted 5 years ago #
perry
Administrator

I'm reworking the uarts as we speak, but currently:

On 2, there's no tx buffer, usart sends are blocking and synchronous.

On 3, see 2, there's no buffer to flush, hence no flush().

4. You can set any rate up to the max of the uart. They aren't required to be fixed, the clock divisors are computed from the entered baud rate. You listed many common rates above. At the moment (as Bryan noted), they're limited to 225000, which is a bug that I didn't catch. There's a fix coming soon.

Error checking is performed, you can't set a baud rate higher than the max baud rate.

5. USART1 tops out at 4.5Mbits/s = 4500000 baud

6. USART2 and USART3 are clocked from the slower APB1 bus, so they top out at 2.5Mbits/s = 2250000 baud.

Posted 5 years ago #
leaflabsandy
Member

Quote: "On 3, see 2, there's no buffer to flush, hence no flush()."

On the Arduino, Serialx.flush always referred to the receive buffer not the transmit buffer!

Note: If you have garbage in the receive buffer you need to flush it out.

Posted 5 years ago #
bnewbold
Ex-Leaflabs

As follow up, we did add a flush() command for the RX buffer in the 0.0.6 version of the IDE.

Posted 5 years ago #
leaflabsandy
Member

IDE 0.0.6

Again ... Again ... Com 2 & 3 = 225 k baud max <-----???
Com 1 = 450 K baud max <-----???
I thought the max. baud problems were fixed!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Why do I get an failed assert error when I put in 256K for com #1?
"Error: Failed Asert: <!baud>usart_Max_baud."

When I get this assert error also I get, for better words, "The Blue LED Status Throbbing Of Death"

Posted 5 years ago #
poslathian
LeafLabs

ew, throbbing of death = assert fail. It sounds like this might just be a bad-assert bug. Ill take a look, thanks!

Posted 5 years ago #

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