FreeCalypso > hg > freecalypso-tools
annotate doc/Flash-boot-modes @ 308:6a254cc6a7f3
doc/Host-tools-overview: fc-cal2bin documented
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Wed, 22 Nov 2017 04:47:36 +0000 |
parents | de8f75783b3b |
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rev | line source |
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Flash-boot-defect and Flash-boot-modes documentation
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1 The Calypso chip includes an on-die boot ROM that allows the boot process to be |
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2 interrupted and diverted by an external host sending some special characters |
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3 into either of the two UARTs; this mechanism is what allows us to load code into |
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4 RAM and to reload the flash on Calypso GSM devices without having to resort to |
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5 JTAG or chip desoldering or other extreme measures. In normal operation, when |
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6 the boot path is NOT being diverted by an external serial download, the boot ROM |
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7 transfers control to the regular firmware in the flash - but there are two |
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8 different modes in which the flash fw image may be booted. |
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9 |
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10 In order for the flash fw image to be considered bootable by the Calypso boot |
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11 ROM, the 32-bit word at flash address 0x2000 must equal either 0 or 1; if it |
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12 equals any other value, the boot ROM will consider the flash fw image to be |
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13 invalid (e.g., blank flash) and will wait forever for a serial download instead |
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14 of proceeding with flash boot. Depending on whether this word at 0x2000 equals |
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15 0 or 1, the flash fw image will be booted in one of two very different ways; |
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16 we shall call them flash boot mode 0 and flash boot mode 1, respectively. |
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17 |
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18 In flash boot mode 0 the following 32-bit word at flash address 0x2004 must |
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19 contain the address of the flash fw image entry point (ARM/Thumb selection in |
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20 the least-significant bit); the boot ROM will simply jump to this address with |
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21 a BX instruction. When the flash fw image is booted in this manner, the boot |
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22 ROM is still mapped at address 0 and the first 8 KiB of flash are inaccessible |
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23 except via the 0x03000000 alternate mapping, unless the firmware later changes |
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24 the 0xFFFFFB10 register. This boot mode is intended for flash fw images that |
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25 use the interrupt and exception vectors in the ROM (branching to IRAM addresses |
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26 0x80001C-0x800034) for their interrupt and exception handling. |
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27 |
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28 Flash boot mode 1 is different: instead of jumping directly to the flash fw |
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29 image, the boot ROM copies a small piece of its code into IRAM and jumps to that |
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30 code; the copied code disables the boot ROM via the 0xFFFFFB10 register (puts |
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31 the external flash at address 0) and induces a processor reset through the |
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32 watchdog timer. It is not clear to us exactly what blocks are affected by the |
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33 watchdog reset, but bits 9:8 of the 0xFFFFFB10 register are not reset, hence |
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34 the ARM processor now boots from the reset vector in the flash as if the boot |
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35 ROM weren't there - and the latter really is not there after having disabled |
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36 itself. |
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37 |
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38 Flash boot mode 0 is only usable on Calypso C035 silicon (the "new" kind); |
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Flash-boot-defect and Flash-boot-modes documentation
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39 while all commercial Calypso GSM devices targeted by FreeCalypso feature Calypso |
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Flash-boot-defect and Flash-boot-modes documentation
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40 chips of the correct "new" kind, the people at TI who wrote and maintained their |
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41 official firmware also had to work with older Calypso C05 chips featured on the |
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42 early D-Sample and Leonardo boards. The earlier boot ROM code version in those |
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43 early Calypso chips also implements the two boot modes which we call mode 0 and |
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44 mode 1, but its implementation of mode 0 is broken and unusable, therefore TI's |
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45 firmware people only used flash boot mode 1. On the other hand, newer firmware |
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46 designs made for current rather than historical hardware will probably find |
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47 mode 0 to be cleaner, more intuitive and more convenient. |
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48 |
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49 All TI official firmwares use flash boot mode 1, our FreeCalypso Magnetite |
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50 firmware does likewise, being a direct derivative of TI's TCS211 fw, but our |
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51 FC Citrine firmware uses flash boot mode 0, as that part of the Citrine fw is |
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52 our own original design. |