elorn-raspi-part-1.lua

require 'sched'
require 'web.server'
require 'web.template'
require 'serial'
telnet = require 'shell.telnet'

uart = serial.open('/dev/ttyAMA0', { baudrate=19200 })

-- Read enough data from the UART to extract two consecutive frames.
function get_raw_data()
  return uart:read(400)
end

-- Return the checksum of the frame between chars #a and #b included.
function frame_checksum(frame, a, b)
  local bytes = { frame:byte(a,b) }
  local sum = 0
  for i=1,#bytes do sum=sum+bytes[i] end
  return sum%256
end

-- Extracts and verifies two consecutive BMV frames from serial data.
function get_frames()
  local REGEXP = '\13\10Checksum\t.()'
  local raw_data = get_raw_data()
  local checksums = { }
  -- find 3 consecutive checksum lines in `raw_data`
  local last_position = 1
  for i=1,3 do
    local next_position = string.match(raw_data, REGEXP, last_position)
    checksums[i]  = next_position
    last_position = next_position
  end
  assert(frame_checksum(raw_data, checksums[1], checksums[2]-1)==0)
  assert(frame_checksum(raw_data, checksums[2], checksums[3]-1)==0)
  return raw_data :sub (checksums[1], checksums[3]-1)
end

-- Converts a pair of frames into a Lua record.
function get_record()
  local frame = get_frames()
  local record = { }
  for line in frame :gmatch "[^\10\13]+" do
    local label, value = line :match '(..-)\t(.+)'
    if label~='Checksum' then
      record[label] = value
    end
  end
  return record
end

-- Serves it as a very crude web page.
web.site[''] = web.template 'default' {
    title = [[Data Monitoring: Elorn's batteries]],
    body = [[
    <table>
      <% for label, value in pairs(get_record()) do %>
      <tr>
        <th><%=label%></th>
        <td><%=value%></td>
      </tr>
      <% end %>
     </table>
     <p><a href=''>Refresh</a></p>
]]}

function main()
  telnet.init{ address='0.0.0.0', port=3000, editmode='edit', historysize=64 }
  web.start(9000)
end

-- Launch the main Lua thread.
sched.run(main)
sched.loop()