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doc/Loadtools-performance: program-m0 slowness documented
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 25 Feb 2020 18:40:00 +0000
parents 39b74c39d914
children 8c6e7b7e701c
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1 Here are the expected run times for the flash dump2bin operation of dumping the
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2 entire flash content of a Calypso GSM device:
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3
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4 Dump of 4 MiB flash (e.g., Openmoko GTA01/02 or Mot C139/140) at 115200 baud:
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5 12m53s
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7 The same 4 MiB flash dump at 812500 baud: 1m50s
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8
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9 Dump of 8 MiB flash (e.g., Mot C155/156) at 812500 baud: 3m40s
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11 Because of the architecture of fc-loadtool and its loadagent back-end, the run
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12 time of a flash dump operation depends only on the serial baud rate and the
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13 size of the flash area to be dumped; it should not depend on the USB-serial
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14 adapter type or any host system properties, as long as the host system and
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15 serial adapter combination supports the desired baud rate. In contrast, flash
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16 programming and fc-xram loading operations are quite different in that their
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17 run times do depend on the host system and USB-serial adapter or other serial
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18 port hardware - this host system dependency exists because of the way these
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19 operations are implemented in our architecture.
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20
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21 Here are some examples of expected flash programming times, all obtained on the
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22 Mother's Slackware 14.2 host system, using the flash program-bin command as
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23 opposed to program-m0 or program-srec:
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25 Flashing an Openmoko GTA02 modem (K5A3281CTM flash chip) with a new firmware
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26 image (2376448 bytes), using a PL2303 USB-serial cable at 115200 baud: 7m35s
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28 Flashing the same OM GTA02 modem with the same fw image, using a CP2102
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29 USB-serial cable at 812500 baud: 1m52s
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31 Flashing a Magnetite hybrid fw image (2378084 bytes) into an FCDEV3B board
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32 (S71PL129N flash chip) via an FT2232D adapter at 812500 baud: 2m11s
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33
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34 These times are just for the flash program-bin operation, not counting the
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35 flash erase which must be done first. Flash erase times are determined
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36 entirely by physical processes inside the flash chip and are not affected by
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37 software design or the serial link: for each sector to be erased, fc-loadtool
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38 issues the sector erase command to the flash chip and then polls the chip for
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39 operation completion status; the polling is done over the serial link and thus
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40 may seem very slow, but the extra bit of latency added by the finite polling
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41 speed is still negligible compared to the time of the actual sector erase
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42 operation inside the flash chip. In contrast, the execution time of a flash
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43 program-bin operation is a sum of 3 components:
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45 * The time it takes for the bits to be transferred over the serial link;
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46 * The time it takes for the flash programming operation to complete on the
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47 target (physics inside the flash chip);
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48 * The overhead of command-response exchanges between fc-loadtool and loadagent.
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49
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50 If you are starting out with a firmware image in m0 format, converting it to
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51 binary with mokosrec2bin (like our FC Magnetite build system always does) and
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52 then flashing via program-bin is faster than flashing the original m0 image
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53 directly via program-m0. Following the last example above of flashing a
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54 Magnetite hybrid fw image into an FCDEV3B, the flashing operation via
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55 program-bin took 2m11s; flashing the same image via program-m0 took 3m54s.
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57 Flashing via program-bin is faster than program-m0 or program-srec because the
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58 program-bin operation uses a larger unit size internally. fc-loadtool
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59 implements all flash programming operations by sending AMFW or INFW commands to
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60 loadagent; each AMFW or INFW command carries a string of 16-bit words to be
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61 programmed. Our program-bin operation programs 256 bytes at a time, i.e.,
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62 sends one AMFW or INFW command per 256 bytes of image payload; our program-m0
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63 and program-srec operations program one S-record at a time, i.e., each S-record
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64 in the source image turns into its own AMFW or INFW command to loadagent. In
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65 the case of m0 images produced by TI's hex470 post-linker, each S-record carries
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66 30 bytes of payload, thus flashing that m0 image directly with program-m0 will
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67 proceed in 30-byte units, whereas converting it to binary and then flashing with
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68 program-bin will proceed in 256-byte units. The smaller unit size slows down
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69 the overall operation by increasing the overhead of command-response exchanges.
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70
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71 XRAM loading via fc-xram is similar to flash program-m0 and program-srec in that
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72 fc-xram sends a separate ML command to loadagent for each S-record, thus the
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73 total XRAM image loading time is not only the serial bit transfer time, but also
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74 the overhead of command-response exchanges between fc-xram and loadagent. Going
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75 back to the same FC Magnetite fw image that can be flashed into an FCDEV3B in
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76 2m11s via program-bin or in 3m54s via program-m0, doing an fc-xram load of that
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77 same fw image (built as ramimage.srec) into the same FCDEV3B via the same
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78 FT2232D adapter at 812500 baud takes 2m54s - thus we can see that fc-xram
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79 loading is faster than flash program-m0 or program-srec, but slower than flash
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80 program-bin.
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81
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82 Why does XRAM loading take longer than flashing? Shouldn't it be faster because
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83 the flash programming step on the target is replaced with a simple memcpy()?
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84 Answer: fc-xram is currently slower than flash program-bin because the latter
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85 sends 256 bytes at a time to loadagent, whereas fc-xram sends one S-record at a
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86 time; the division of the image into S-records is determined by the tool that
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87 generates the SREC image, but TI's hex470 post-linker generates images with 30
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88 bytes of payload per S-record. Having the operation proceed in smaller chunks
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89 increases the overhead of command-response exchanges and thus increases the
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90 overall time.