Hi Johan, Sorry for the slow reply. Thanks for the feedback. I've amended the patch and is below. I think I've done all of your suggestions and looks more Linux Kernelish style. > drop the denom outmost parenthesis (also in some expressions below) I removed the outmost parenthesis from the " denom = " line but wasn't too sure what the "some expressions below" were. int only guarantees 16bits so that's why I went for ones of the form long/s32/int32_t for some variables. I noticed that other things like "priv->baud_rate" for example is an unsigned int so that wouldn't work for some 16bit systems (such as the dsPIC with xc16) for speeds beyond 65KBaud. Here's the amended patch, any feedback greatly appreciated... For some wanted baud rates ch341_set_baudrate_lcr() calculates the "a" value such that it produces a significantly different baud rate than the desired one. This means some hardware can't communicate with the CH34x chip. Particularly obvious wrong baud rates are 256000 and 921600 which deviate by 2.3% and 7.4% respectively. This proposed patch will bring the errors for these baud rates to below 0.5%. This patch will significantly improve the error of some other unusual baud rates too (such as 1333333 from 10% error to 0% error). Currently ch341_set_baudrate_lcr() will accept any baud rate and can produce a practically arbitrary large error (for example a 40% error for 5000000). This patch does not address this issue. The patch has been tested on two computers and only with the CH340G chip. With a CH340G chip with "Chip version: 0x31" on a JPIC I tested the bitrate error using a RIGOL DS1054 scope without the patch and measured the following... Baud wanted Baud measured Error as % of wanted 50 50 0.0% 75 75.2 0.3% 110 109.5 0.5% 135 134.6 0.3% 150 150.4 0.3% 300 300.8 0.3% 600 601.3 0.2% 1200 1201.9 0.2% 1800 1801.8 0.1% 2400 2403.8 0.2% 4800 4807.7 0.2% 7200 7215 0.2% 9600 9615.4 0.2% 14400 14430 0.2% 19200 19231 0.2% 38400 38462 0.2% 56000 56054 0.1% 57600 57837 0.4% 115200 115207 0.0% 128000 127551 0.4% 230400 230415 0.0% 256000 250000 2.3% 460800 460617 0.0% 921600 853242 7.4% 1000000 999001 0.1% 1333333 1204819 9.6% 1843200 1496334 18.8% 2000000 1984127 0.8% 5000000 2985075 40.3% Measurements and working as a libre/open office document can be found at https://jontio.github.io/linux_kernel_work/ch43x_tests.ods Signed-off-by: Jonathan Olds <jontio@xxxxxxxxxxxx> --- drivers/usb/serial/ch341.c | 46 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c index 3bb1fff02bed..5ef8db2974d5 100644 --- a/drivers/usb/serial/ch341.c +++ b/drivers/usb/serial/ch341.c @@ -54,6 +54,11 @@ #define CH341_BAUDBASE_FACTOR 1532620800 #define CH341_BAUDBASE_DIVMAX 3 +/* Chip frequency is 12Mhz. not quite the same as + * (CH341_BAUDBASE_FACTOR>>7) + */ +#define CH341_OSC_FREQUENCY 12000000 + /* Break support - the information used to implement this was gleaned from * the Net/FreeBSD uchcom.c driver by Takanori Watanabe. Domo arigato. */ @@ -151,6 +156,9 @@ static int ch341_set_baudrate_lcr(struct usb_device *dev, int r; unsigned long factor; short divisor; + u8 msb; + s32 baud_wanted; + u32 denom; if (!priv->baud_rate) return -EINVAL; @@ -168,6 +176,44 @@ static int ch341_set_baudrate_lcr(struct usb_device *dev, factor = 0x10000 - factor; a = (factor & 0xff00) | divisor; + /* + * Calculate baud error using the 0,1,2,3 lsb and + * also the error without the divisor (lsb==7). + * Decide whether the divisor should be used. + */ + msb = (a >> 8) & 0xff; + baud_wanted = priv->baud_rate; + denom = (1ul << (10 - 3 * (divisor & 0x03))) * (256 - msb); + /* + * baud_wanted==(CH341_OSC_FREQUENCY/256) implies msb==0 for no divisor + * the 100 is for rounding. + */ + if (denom && ((baud_wanted + 100) >= (((u32)CH341_OSC_FREQUENCY) >> 8))) { + /* Calculate error for divisor */ + long baud_expected = ((u32)CH341_OSC_FREQUENCY) / denom; + u32 baud_error_difference = abs(baud_expected-baud_wanted); + + /* Calculate a for no divisor */ + u32 a_no_divisor = ((0x10000 - (((u32)CH341_OSC_FREQUENCY) << 8) / + baud_wanted + 128) & 0xff00) | 0x07; + + /* a_no_divisor is only valid for msb<248 */ + if ((a_no_divisor >> 8) < 248) { + /* Calculate error for no divisor */ + long baud_expected_no_divisor = ((u32)CH341_OSC_FREQUENCY) / + (256 - (a_no_divisor >> 8)); + u32 baud_error_difference_no_divisor = + abs(baud_expected_no_divisor-baud_wanted); + + /* + * If error using no divisor is less than using + * a divisor then use it instead for the "a" word. + */ + if (baud_error_difference_no_divisor < baud_error_difference) + a = a_no_divisor; + } + } + /* * CH341A buffers data until a full endpoint-size packet (32 bytes) * has been received unless bit 7 is set. -- 2.17.1 Cheers, Jonti -----Original Message----- From: Johan Hovold [mailto:johan@xxxxxxxxxx] Sent: Friday, 21 June 2019 1:43 a.m. To: jontio Cc: johan@xxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx Subject: Re: [PATCH] USB: serial: ch341: fix wrong baud rate setting calculation On Sat, Jun 08, 2019 at 05:13:09PM +1200, jontio wrote: > For some wanted baud rates ch341_set_baudrate_lcr() calculates the "a" > value such that it produces a significantly different baud rate than > the desired one. This means some hardware can't communicate with the > CH34x chip. Particularly obvious wrong baud rates are 256000 and > 921600 which deviate by 2.3% and 7.4% respectively. This proposed > patch will bring the errors for these baud rates to below 0.5%. This > patch will significantly improve the error of some other unusual baud > rates too (such as 1333333 from 10% error to 0% error). Currently > ch341_set_baudrate_lcr() will accept any baud rate and can produce a > practically arbitrary large error (for example a 40% error for > 5000000) this patch does not address this issue. It doesn't hurt to expand the commit message with further details from your other mail. > Signed-off-by: jontio <jontio@xxxxxxxxxxxx> You need to sign off with your full name. It should also match the From line (author). > --- > drivers/usb/serial/ch341.c | 45 > ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 45 insertions(+) > > diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c > index 3bb1fff02bed..7cd1d6f70b56 100644 > --- a/drivers/usb/serial/ch341.c > +++ b/drivers/usb/serial/ch341.c > @@ -54,6 +54,9 @@ > #define CH341_BAUDBASE_FACTOR 1532620800 #define > CH341_BAUDBASE_DIVMAX 3 > > +/* Chip frequency is 12Mhz. not quite the same as > +(CH341_BAUDBASE_FACTOR>>7) */ #define CH341_OSC_FREQUENCY 12000000 > + > /* Break support - the information used to implement this was gleaned from > * the Net/FreeBSD uchcom.c driver by Takanori Watanabe. Domo arigato. > */ > @@ -168,6 +171,48 @@ static int ch341_set_baudrate_lcr(struct usb_device *dev, > factor = 0x10000 - factor; > a = (factor & 0xff00) | divisor; > > + /* > + * Calculate baud error using the 0,1,2,3 LSB and > + * also the error without the divisor (LSB==7). > + * Decide whether the divisor should be used. Wrap also comments at 72 cols or so. > + */ > + uint32_t msB = (a>>8) & 0xFF; > + uint32_t lsB = a & 0xFF; > + int32_t baud_wanted = priv->baud_rate; > + uint32_t denom = ((1<<(10-3*lsB))*(256-msB)); It's not obvious from just looking at the above chunk that 3*lsB < 10. And some style issues: - declare variables at the start of the function (or possibly start of block), and defer non-trivial initialisation - use the kernel types u32, s32 or plain (unsigned) int instead of the c99 types. - no camel case, msb, lsb is fine - add a space on both sides of operators (also in your comments) - drop the denom outmost parenthesis (also in some expressions below) - please use lowercase hex notation for consistency with the rest of the driver (function) > + /* > + * baud_wanted==(CH341_OSC_FREQUENCY/256) implies MSB==0 for no divisor > + * the 100 is for rounding. > + */ > + if (denom && ((baud_wanted+100) >= > +(((uint32_t)CH341_OSC_FREQUENCY)>>8))) { > + > + /* Calculate error for divisor */ > + int32_t baud_expected = ((uint32_t)CH341_OSC_FREQUENCY) / denom; > + uint32_t baud_error_difference = abs(baud_expected-baud_wanted); > + > + /* Calculate a for no divisor */ > + uint32_t a_no_divisor = ((0x10000-(((uint32_t)CH341_OSC_FREQUENCY)<<8) / > + baud_wanted+128) & 0xFF00) | 0x07; > + > + /* a_no_divisor is only valid for MSB<248 */ > + if ((a_no_divisor>>8) < 248) { > + > + /* Calculate error for no divisor */ > + int32_t baud_expected_no_divisor = ((uint32_t)CH341_OSC_FREQUENCY) / > + (256-(a_no_divisor>>8)); > + uint32_t baud_error_difference_no_divisor = > + abs(baud_expected_no_divisor-baud_wanted); > + > + /* > + * If error using no divisor is less than using > + * a divisor then use it instead for the "a" word. > + */ > + if (baud_error_difference_no_divisor < baud_error_difference) > + a = a_no_divisor; > + } > + Stray newline. > + } > + > /* > * CH341A buffers data until a full endpoint-size packet (32 bytes) > * has been received unless bit 7 is set. Ok, I'm gonna have to look at this again, but perhaps you can consider the style input meanwhile. Johan
