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| author | Daniel Friesel <derf@finalrewind.org> | 2022-05-26 10:18:18 +0200 |
|---|---|---|
| committer | Daniel Friesel <derf@finalrewind.org> | 2022-05-26 10:18:18 +0200 |
| commit | 3aabcac3aa26b40b2712928b74e6bbfdf4f3efb4 (patch) | |
| tree | 9866583efeb5bd7cd543d5efc688ce70322924c1 | |
| parent | 3f09903d71fd2e16d1702e21c1572269c67cb47b (diff) | |
Verify CRC when reading data
| -rw-r--r-- | README.md | 1 | ||||
| -rw-r--r-- | sen5x.lua | 31 |
2 files changed, 32 insertions, 0 deletions
@@ -10,6 +10,7 @@ sen5x.lua has been tested with Lua 5.1 on NodeMCU firmware 3.0.1 (Release 202112300746, integer build). It requires the following modules. * i2c +* bit The MQTT HomeAssistant integration in init.lua additionally needs the following modules. @@ -48,6 +48,9 @@ function sen5x.read() end local data = i2c.read(sen5x.bus_id, 24) i2c.stop(sen5x.bus_id) + if not sen5x.crc_valid(data, 24) then + return false + end sen5x.pm1 = sen5x.read_value(data, 1) sen5x.pm2_5 = sen5x.read_value(data, 4) sen5x.pm4 = sen5x.read_value(data, 7) @@ -76,6 +79,9 @@ function sen5x.get_product() end local data = i2c.read(sen5x.bus_id, 48) i2c.stop(sen5x.bus_id) + if not sen5x.crc_valid(data, 48) then + return false + end local ret = "" ret = ret .. string.sub(data, 1, 2) ret = ret .. string.sub(data, 4, 5) @@ -83,4 +89,29 @@ function sen5x.get_product() return ret end +function sen5x.crc_word(data, index) + local crc = 0xff + for i = index, index+1 do + crc = bit.bxor(crc, string.byte(data, i)) + for j = 8, 1, -1 do + if bit.isset(crc, 7) then + crc = bit.bxor(bit.lshift(crc, 1), 0x31) + else + crc = bit.lshift(crc, 1) + end + crc = bit.band(crc, 0xff) + end + end + return bit.band(crc, 0xff) +end + +function sen5x.crc_valid(data, length) + for i = 1, length, 3 do + if sen5x.crc_word(data, i) ~= string.byte(data, i+2) then + return false + end + end + return true +end + return sen5x |