diff options
| author | Yurii Soldak <[email protected]> | 2023-12-04 01:30:31 +0100 |
|---|---|---|
| committer | Ron Evans <[email protected]> | 2023-12-05 16:29:51 +0100 |
| commit | 338590cc7505bc529e98b122b39460d5fb3a13be (patch) | |
| tree | 678c738238c009a1a06df43b5c4dd7ef0419bdb1 /src | |
| parent | 22d70604d841aa01319a9b9ff0231763f77fabb4 (diff) | |
| download | tinygo-338590cc7505bc529e98b122b39460d5fb3a13be.tar.gz tinygo-338590cc7505bc529e98b122b39460d5fb3a13be.zip | |
machine/atmega: uart double speed mode
Less errors and higher throughput.
Example: default / slow mode is problematic for 115200 on 16Mhz CPU.
Diffstat (limited to 'src')
| -rw-r--r-- | src/machine/machine_atmega.go | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/src/machine/machine_atmega.go b/src/machine/machine_atmega.go index f1838a08a..46dee5ef1 100644 --- a/src/machine/machine_atmega.go +++ b/src/machine/machine_atmega.go @@ -179,10 +179,18 @@ func (uart *UART) Configure(config UARTConfig) { config.BaudRate = 9600 } - // Set baud rate based on prescale formula from - // https://www.microchip.com/webdoc/AVRLibcReferenceManual/FAQ_1faq_wrong_baud_rate.html - // ((F_CPU + UART_BAUD_RATE * 8L) / (UART_BAUD_RATE * 16L) - 1) - ps := ((CPUFrequency()+config.BaudRate*8)/(config.BaudRate*16) - 1) + // Prescale formula for u2x mode from AVR MiniCore source code. + // Same as formula from specification but taking into account rounding error. + ps := (CPUFrequency()/4/config.BaudRate - 1) / 2 + uart.statusRegA.SetBits(avr.UCSR0A_U2X0) + + // Hardcoded exception for 57600 for compatibility with older bootloaders. + // Also, prescale cannot be > 4095, so switch back to non-u2x mode if the baud rate is too low. + if (CPUFrequency() == 16000000 && config.BaudRate == 57600) || ps > 0xfff { + ps = (CPUFrequency()/8/config.BaudRate - 1) / 2 + uart.statusRegA.ClearBits(avr.UCSR0A_U2X0) + } + uart.baudRegH.Set(uint8(ps >> 8)) uart.baudRegL.Set(uint8(ps & 0xff)) |