From: Adrian Negreanu Date: Mon, 7 Sep 2020 19:36:10 +0000 (+0300) Subject: drivers/jlink: fix calculate_swo_prescaler formula X-Git-Url: https://git.gag.com/?a=commitdiff_plain;h=051e80812b1b3bb4deabef272c12bb95f10748da;p=fw%2Fopenocd drivers/jlink: fix calculate_swo_prescaler formula a) TPIU_ACPR is defined as: SWO_baudrate = TRACECLKIN/(TPIU_ACPR +1) b) TPIU_ACPR is set by armv7m_trace_tpiu_config() target_write_u32(target, TPIU_ACPR, Prescaler-1), so TPIU_ACPR = Prescaler-1 Replacing TPIU_ACPR in a), we get: SWO_baudrate = TRACECLKIN/Prescaler, so c) Prescaler = TRACECLKIN/SWO_baudrate The Prescaler calculated by calculate_swo_prescaler() is greater by 1: Prescaler = TRACECLKIN/SWO_baudrate + 1 The second problem is that even in situations when an exact baudrate match is possible, the resulting TRACECLKIN/Prescaler already has a 3% deviation. For example, TRACECLKIN=88000000, SWO_baudrate=500000, calculate_swo_prescaler will return Prescaler=171. The correct value should be Prescaler=176 (TPIU_ACPR=175). Might be related to https://sourceforge.net/p/openocd/tickets/263/ Change-Id: Ib4d6df6e34685a9be4c2995cb500b2411c76e39b Signed-off-by: Adrian Negreanu Reviewed-on: http://openocd.zylin.com/5807 Tested-by: jenkins Reviewed-by: Marc Schink Reviewed-by: Antonio Borneo --- diff --git a/src/jtag/drivers/jlink.c b/src/jtag/drivers/jlink.c index 57e357b79..910799ce2 100644 --- a/src/jtag/drivers/jlink.c +++ b/src/jtag/drivers/jlink.c @@ -1270,16 +1270,14 @@ static bool calculate_swo_prescaler(unsigned int traceclkin_freq, uint32_t trace_freq, uint16_t *prescaler) { unsigned int presc; - double deviation; - - presc = ((1.0 - SWO_MAX_FREQ_DEV) * traceclkin_freq) / trace_freq + 1; - + presc = DIV_ROUND_UP(traceclkin_freq, trace_freq); if (presc > TPIU_ACPR_MAX_SWOSCALER) return false; - deviation = fabs(1.0 - ((double)trace_freq * presc / traceclkin_freq)); - - if (deviation > SWO_MAX_FREQ_DEV) + /* Probe's UART speed must be within 3% of the TPIU's SWO baud rate. */ + unsigned int max_deviation = (traceclkin_freq * 3) / 100; + if (presc * trace_freq < traceclkin_freq - max_deviation || + presc * trace_freq > traceclkin_freq + max_deviation) return false; *prescaler = presc;