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libsigrok/src/dmm/bm85x.c

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/*
* This file is part of the libsigrok project.
*
* Copyright (C) 2012 Alexandru Gagniuc <mr.nuke.me@gmail.com>
* Copyright (C) 2014 Aurelien Jacobs <aurel@gnuage.org>
* Copyright (C) 2019-2020 Gerhard Sittig <gerhard.sittig@gmx.net>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* @file
*
* Protocol parser for Brymen BM850s DMM packets. The USB protocol (for the
* cable) and the packet description (for the meter) were retrieved from:
* http://brymen.com/product-html/Download2.html
* http://brymen.com/product-html/PD02BM850s_protocolDL.html
* http://brymen.com/product-html/images/DownloadList/ProtocolList/BM850-BM850a-BM850s_List/BM850-BM850a-BM850s-500000-count-DMM-protocol-BC85X-BC85Xa.zip
*
* Implementor's notes on the protocol:
* - The BM85x devices require a low RTS pulse after COM port open and
* before communication of requests and responses. The vendor doc
* recommends 100ms pulse width including delays around it. Without
* that RTS pulse the meter won't respond to requests.
* - The request has a three byte header (DLE, STX, command code), two
* bytes command arguments, and three bytes tail (checksum, DLE, ETX).
* The checksum spans the area (including) the command code and args.
* The checksum value is the XOR across all payload bytes. Exclusively
* command 0x00 is used (initiate next measurement response) which does
* not need arguments (passes all-zero values).
* - The response has a four byte header (DLE, STX, command code, payload
* size), the respective number of payload data bytes, and a three byte
* tail (checksum, DLE, ETX). The checksum spans the range after the
* length field and before the checksum field. Command 0 response data
* payload consists of a four byte flags field and a text field for
* measurement values (floating point with exponent in ASCII).
* - Special cases of response data:
* - The text field which carries the measurement value also contains
* whitespace which may break simple text to number conversion. Like
* 10 02 00 0f 07 00 00 00 20 30 2e 30 30 33 32 20 45 2b 30 46 10 03
* which translates to: 07 00 00 00 " 0.0032 E+0". Text for overload
* conditions can be shorter which results in variable packet length.
* Some meter functions provide unexpected text for their values.
* - The reference impedance for decibel measurements looks wrong and
* requires special treatment to isolate the 4..1200R value:
* bfunc 80 20 00 00, text " 0. 800 E+1" (reference, 800R)
* The decibel measurement values use an unexpected scale.
* bfunc 00 20 00 00, text "-0.3702 E-1" (measurement, -37.02dBm)
* The reference value gets sent (sometimes) in a DMM response when
* the meter's function is entered, or the reference value changes.
* The 'bfunc' flags combination allows telling packet types apart.
* - Temperature measurements put the C/F unit between the mantissa
* and the exponent, which needs to get removed: " 0.0217CE+3"
* - Diode measurements appear to exclusively provide the 'Volt' flag
* but no 'Diode' flag. The display shows ".diod" for a moment but
* this information is no longer available when voltage measurements
* are seen.
*/
#include <config.h>
#include <ctype.h>
#include <math.h>
#include <libsigrok/libsigrok.h>
#include "libsigrok-internal.h"
#include <string.h>
#define LOG_PREFIX "brymen-bm85x"
#define STX 0x02
#define ETX 0x03
#define DLE 0x10
#define CMD_GET_READING 0
#define PKT_HEAD_LEN 4
#define PKT_DATA_MAX 15
#define PKT_TAIL_LEN 3
#define PKT_BFUNC_LEN 4
static uint8_t bm85x_crc(const uint8_t *buf, size_t len)
{
uint8_t crc;
crc = 0;
while (len--)
crc ^= *buf++;
return crc;
}
#ifdef HAVE_SERIAL_COMM
/** Meter's specific activity after port open and before data exchange. */
SR_PRIV int brymen_bm85x_after_open(struct sr_serial_dev_inst *serial)
{
int rts_toggle_delay_us;
/*
* The device requires an RTS *pulse* before communication.
* The vendor's documentation recommends the following sequence:
* Open the COM port, wait for 100ms, set RTS=1, wait for 100ms,
* set RTS=0, wait for 100ms, set RTS=1, configure bitrate and
* frame format, transmit request data, receive response data.
*/
rts_toggle_delay_us = 100 * 1000; /* 100ms */
g_usleep(rts_toggle_delay_us);
serial_set_handshake(serial, 1, -1);
g_usleep(rts_toggle_delay_us);
serial_set_handshake(serial, 0, -1);
g_usleep(rts_toggle_delay_us);
serial_set_handshake(serial, 1, -1);
g_usleep(rts_toggle_delay_us);
return SR_OK;
}
static int bm85x_send_command(struct sr_serial_dev_inst *serial,
uint8_t cmd, uint8_t arg1, uint8_t arg2)
{
uint8_t buf[8];
uint8_t crc, *wrptr, *crcptr;
size_t wrlen;
int ret;
wrptr = &buf[0];
write_u8_inc(&wrptr, DLE);
write_u8_inc(&wrptr, STX);
crcptr = wrptr;
write_u8_inc(&wrptr, cmd);
write_u8_inc(&wrptr, arg1);
write_u8_inc(&wrptr, arg2);
crc = bm85x_crc(crcptr, wrptr - crcptr);
write_u8_inc(&wrptr, crc);
write_u8_inc(&wrptr, DLE);
write_u8_inc(&wrptr, ETX);
wrlen = wrptr - &buf[0];
ret = serial_write_nonblocking(serial, &buf[0], wrlen);
if (ret < 0)
return ret;
if ((size_t)ret != wrlen)
return SR_ERR_IO;
return SR_OK;
}
/** Initiate reception of another meter's reading. */
SR_PRIV int brymen_bm85x_packet_request(struct sr_serial_dev_inst *serial)
{
return bm85x_send_command(serial, CMD_GET_READING, 0, 0);
}
#endif
/**
* Check Brymen BM85x DMM packet for validity.
*
* @param[in] st The DMM driver's internal state.
* @param[in] buf The data bytes received so far.
* @param[in] len The received data's length (byte count).
* @param[out] pkt_len The packet's calculated total size (when valid).
*
* The BM850s protocol uses packets of variable length. A minimum amount
* of RX data provides the packet header, which communicates the payload
* size, which allows to determine the packet's total size. Callers of
* this validity checker can learn how much data will get consumed when
* a valid packet got received and processed. The packet size is not
* known in advance.
*
* @returns SR_OK when the packet is valid.
* @returns SR_ERR* (below zero) when the packet is invalid.
* @returns Greater 0 when packet is incomplete, more data is needed.
*/
SR_PRIV int brymen_bm85x_packet_valid(void *st,
const uint8_t *buf, size_t len, size_t *pkt_len)
{
size_t plen;
uint8_t cmd, crc;
(void)st;
/* Four header bytes: DLE, STX, command, payload length. */
if (len < PKT_HEAD_LEN)
return SR_PACKET_NEED_RX;
if (read_u8_inc(&buf) != DLE)
return SR_PACKET_INVALID;
if (read_u8_inc(&buf) != STX)
return SR_PACKET_INVALID;
cmd = read_u8_inc(&buf);
/* Non-fatal, happens with OL pending during connect. */
if (cmd == 0x01)
cmd = 0x00;
if (cmd != CMD_GET_READING)
return SR_PACKET_INVALID;
plen = read_u8_inc(&buf);
if (plen > PKT_DATA_MAX)
return SR_PACKET_INVALID;
len -= PKT_HEAD_LEN;
/* Checksum spans bfunc and value text. Length according to header. */
if (len < plen + PKT_TAIL_LEN)
return SR_PACKET_NEED_RX;
crc = bm85x_crc(buf, plen);
buf += plen;
len -= plen;
/* Three tail bytes: checksum, DLE, ETX. */
if (len < PKT_TAIL_LEN)
return SR_PACKET_NEED_RX;
if (read_u8_inc(&buf) != crc)
return SR_PACKET_INVALID;
if (read_u8_inc(&buf) != DLE)
return SR_PACKET_INVALID;
if (read_u8_inc(&buf) != ETX)
return SR_PACKET_INVALID;
/*
* Only return the total packet length when the receive buffer
* was found to be valid. For invalid packets it's preferred to
* have the caller keep trying to sync to the packet stream.
*/
if (pkt_len)
*pkt_len = PKT_HEAD_LEN + plen + PKT_TAIL_LEN;
return SR_PACKET_VALID;
}
struct bm85x_flags {
gboolean is_batt, is_db, is_perc, is_hz, is_amp, is_beep;
gboolean is_ohm, is_temp_f, is_temp_c, is_diode, is_cap;
gboolean is_volt, is_dc, is_ac;
};
static int bm85x_parse_flags(const uint8_t *bfunc, struct bm85x_flags *flags)
{
if (!bfunc || !flags)
return SR_ERR_ARG;
memset(flags, 0, sizeof(*flags));
flags->is_batt = bfunc[3] & (1u << 7);
if ((bfunc[3] & 0x7f) != 0)
return SR_ERR_ARG;
if ((bfunc[2] & 0xff) != 0)
return SR_ERR_ARG;
if ((bfunc[1] & 0xc0) != 0)
return SR_ERR_ARG;
flags->is_db = bfunc[1] & (1u << 5);
if ((bfunc[1] & 0x10) != 0)
return SR_ERR_ARG;
flags->is_perc = bfunc[1] & (1u << 3);
flags->is_hz = bfunc[1] & (1u << 2);
flags->is_amp = bfunc[1] & (1u << 1);
flags->is_beep = bfunc[1] & (1u << 0);
flags->is_ohm = bfunc[0] & (1u << 7);
flags->is_temp_f = bfunc[0] & (1u << 6);
flags->is_temp_c = bfunc[0] & (1u << 5);
flags->is_diode = bfunc[0] & (1u << 4);
flags->is_cap = bfunc[0] & (1u << 3);
flags->is_volt = bfunc[0] & (1u << 2);
flags->is_dc = bfunc[0] & (1u << 1);
flags->is_ac = bfunc[0] & (1u << 0);
return SR_OK;
}
static int bm85x_parse_value(char *txt, double *val, int *digits)
{
char *src, *dst, c;
int ret;
/*
* See above comment on whitespace in response's number text.
* The caller provides a NUL terminated writable text copy.
* Go for low hanging fruit first (OL condition). Eliminate
* whitespace then and do the number conversion.
*/
if (strstr(txt, "+OL")) {
*val = +INFINITY;
return SR_OK;
}
if (strstr(txt, "-OL")) {
*val = -INFINITY;
return SR_OK;
}
if (strstr(txt, "OL")) {
*val = INFINITY;
return SR_OK;
}
src = txt;
dst = txt;
while (*src) {
c = *src++;
if (c == ' ')
continue;
*dst++ = c;
}
*dst = '\0';
ret = sr_atod_ascii_digits(txt, val, digits);
if (ret != SR_OK)
return ret;
return SR_OK;
}
static int bm85x_parse_payload(const uint8_t *p, size_t l,
double *val, struct sr_datafeed_analog *analog)
{
const uint8_t *bfunc;
char text_buf[PKT_DATA_MAX], *text;
size_t text_len;
int ret;
struct bm85x_flags flags;
int digits;
char *parse;
/* Get a bfunc bits reference, and a writable value text. */
bfunc = &p[0];
text_len = l - PKT_BFUNC_LEN;
memcpy(text_buf, &p[PKT_BFUNC_LEN], text_len);
text_buf[text_len] = '\0';
text = &text_buf[0];
sr_dbg("DMM bfunc %02x %02x %02x %02x, text \"%s\"",
bfunc[0], bfunc[1], bfunc[2], bfunc[3], text);
/* Check 'bfunc' bitfield first, text interpretation depends on it. */
ret = bm85x_parse_flags(bfunc, &flags);
if (ret != SR_OK)
return ret;
/* Parse the text after potential normalization/transformation. */
if (flags.is_db && flags.is_ohm) {
static const char *prefix = " 0.";
static const char *suffix = " E";
/* See above comment on dBm reference value text. */
if (strncmp(text, prefix, strlen(prefix)) != 0)
return SR_ERR_DATA;
text += strlen(prefix);
text_len -= strlen(prefix);
parse = strstr(text, suffix);
if (!parse)
return SR_ERR_DATA;
*parse = '\0';
}
if (flags.is_temp_f || flags.is_temp_c) {
/* See above comment on temperature value text. */
parse = strchr(text, flags.is_temp_f ? 'F' : 'C');
if (!parse)
return SR_ERR_DATA;
*parse = ' ';
}
digits = 0;
ret = bm85x_parse_value(text, val, &digits);
if (ret != SR_OK)
return ret;
/* Fill in MQ and flags result details. */
analog->meaning->mqflags = 0;
if (flags.is_volt) {
analog->meaning->mq = SR_MQ_VOLTAGE;
analog->meaning->unit = SR_UNIT_VOLT;
}
if (flags.is_amp) {
analog->meaning->mq = SR_MQ_CURRENT;
analog->meaning->unit = SR_UNIT_AMPERE;
}
if (flags.is_ohm) {
if (flags.is_db)
analog->meaning->mq = SR_MQ_RESISTANCE;
else if (flags.is_beep)
analog->meaning->mq = SR_MQ_CONTINUITY;
else
analog->meaning->mq = SR_MQ_RESISTANCE;
analog->meaning->unit = SR_UNIT_OHM;
}
if (flags.is_hz) {
analog->meaning->mq = SR_MQ_FREQUENCY;
analog->meaning->unit = SR_UNIT_HERTZ;
}
if (flags.is_perc) {
analog->meaning->mq = SR_MQ_DUTY_CYCLE;
analog->meaning->unit = SR_UNIT_PERCENTAGE;
}
if (flags.is_cap) {
analog->meaning->mq = SR_MQ_CAPACITANCE;
analog->meaning->unit = SR_UNIT_FARAD;
}
if (flags.is_temp_f) {
analog->meaning->mq = SR_MQ_TEMPERATURE;
analog->meaning->unit = SR_UNIT_FAHRENHEIT;
}
if (flags.is_temp_c) {
analog->meaning->mq = SR_MQ_TEMPERATURE;
analog->meaning->unit = SR_UNIT_CELSIUS;
}
if (flags.is_db && !flags.is_ohm) {
/* See above comment on dBm measurements scale. */
analog->meaning->mq = SR_MQ_POWER;
analog->meaning->unit = SR_UNIT_DECIBEL_MW;
*val *= 1000;
digits -= 3;
}
if (flags.is_diode) {
/* See above comment on diode measurement responses. */
analog->meaning->mq = SR_MQ_VOLTAGE;
analog->meaning->unit = SR_UNIT_VOLT;
analog->meaning->mqflags |= SR_MQFLAG_DIODE;
analog->meaning->mqflags |= SR_MQFLAG_DC;
}
if (flags.is_ac)
analog->meaning->mqflags |= SR_MQFLAG_AC;
if (flags.is_dc)
analog->meaning->mqflags |= SR_MQFLAG_DC;
analog->encoding->digits = digits;
analog->spec->spec_digits = digits;
if (flags.is_batt)
sr_warn("Low battery!");
return SR_OK;
}
SR_PRIV int brymen_bm85x_parse(void *st, const uint8_t *buf, size_t len,
double *val, struct sr_datafeed_analog *analog, void *info)
{
const uint8_t *pl_ptr;
size_t pl_len;
(void)st;
(void)info;
if (!buf || !len)
return SR_ERR_DATA;
if (!val || !analog)
return SR_ERR_DATA;
if (brymen_bm85x_packet_valid(NULL, buf, len, NULL) != SR_PACKET_VALID)
return SR_ERR_DATA;
pl_ptr = &buf[PKT_HEAD_LEN];
pl_len = len - PKT_HEAD_LEN - PKT_TAIL_LEN;
return bm85x_parse_payload(pl_ptr, pl_len, val, analog);
}
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