47 lines
1.3 KiB
Plaintext
47 lines
1.3 KiB
Plaintext
STC15 series USB ISP protocol
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=============================
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General principle
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-----------------
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- host does OUT and IN control transfers for write and read
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- IN transfer with wLength = 132, wValue = 0, wIndex = 0, bRequest = 0 are used for all reads
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- OUT transfers with with specific bRequest, wValue, wIndex are used for writes
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Packet coding
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-------------
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- packets from MCU
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always start with 0x46 0xb9, similar to serial protocols
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third byte is packet length, followed by data bytes
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checksum at the end: 8 bit modular sum
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- packets from host
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no header bytes
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bRequest sets packet type
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wValue, wIndex interpretation according to packet type
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8 bit modular checksum for every 7 bytes, interleaved
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- packet types derived from the serial protocol
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Specific packet information
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---------------------------
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- flash data
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wIndex specifies write address
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wValue is 0xa55a
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bRequest is 0x22 for first packet, 0x02 for the following ones
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unusually encoded: a total of 128 bytes per packet,
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with every 7 byte checksummed in some way,
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for a total of 18x7 byte segments and a final 2 byte segment
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checksum: 8 bit modular sum
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- option packet
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generally same as with serial protocol, some header stuff omitted
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wIndex is 0
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wValue is 0xa55a
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bRequest is 4
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seems to use the same checksumming scheme as flash writes
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