72 lines
2.9 KiB
Plaintext
72 lines
2.9 KiB
Plaintext
USB Blaster Cheap Clone
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=======================
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The Altera USB Blaster has a cheap clone, based on :
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- a Cypress CY7C68013A-56PVXC as the main chip
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- a 74HC244D as the output latch
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- a 24 MHz quartz
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- a EEPROM 24C64BN
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The schematics (cut down to essential) is :
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/-----------------+----------------------\
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+--------------+ | | |
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USB--| CY7C68013A | | +----------+ | |
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| | | | 74HC244D | | |
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. . | | | | |
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. . \--o 1 20 o | 10 pins header |
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| 47 o-- TCK --o 2 19 o---/ +-------+ |
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| 46 o-- TDO --o 3 18 o-- TCK -----o 1 2 o |
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| 45 o-- TMS --o 4 17 o-- TDO -----o 3 4 o |
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| 44 o o 5 16 o-- TMS -----o 5 6 o |
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| 43 o-- o 6 15 o o 7 8 o |
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| 42 o-- o 7 14 o +--o 9 10 o |
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| 41 o-- TDI --o 8 13 o-- ? | +-------+ |
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. 40 o-- nOE \ o 9 12 o-- TDI --+ |
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. . | o 10 11 o |
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o 28 29 o | | | |
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| | | +----------+ |
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+--------------+ \ |
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---------------------------------------/
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From this one can deduce that :
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- the cypress emulates the Altera chip
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- as the cypress pins used are 41-47, all output/input are controlled by 8051
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PortA.
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- as the 8051 is clocked at 24Mhz, and because each USB byte is handled by the
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8051, assuming a 40 instruction cycles per USB packet, the maximum throughput
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would be around 500 kHz.
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Pinout
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======
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Port A.0: nOE (output enable of 74HC244D)
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Port A.1: TDI
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Port A.5: TMS
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Port A.6: TDO
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Port A.7: TCK
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Throughput considerations
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=========================
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Measurements on a scope reveal that :
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- for bitbang mode, the throughput is 56.5 kbits/s
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(as each clock transition is measured at 17.7us)
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- for byteshift mode, the throughput is 107.7 kbits/s
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(as 63 bits TDI transmission is measured in 585 us)
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Let's suppose that to upload a 32 bits value, it is necessary to :
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- move from IDLE to DR-SHIFT : 3 bitbang (3 TMS transitions)
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- input the 32 bits of data : 1 byteshift (24 bits) + 8 bitbang (8 bits)
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- move from DR-SHIFT to IDLE : 5 bitbang (5 TMS transitions)
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So for this 32 bits of data, the time would be :
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3 * 17.7us + 1 * 585us/63*24 + 5 * 17.7us
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= 53.1us + 222us + 88.5us
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= 363us
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Throughput in bit/s: 32 * (1 / 363E-6) = 88000 bits/s
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Throughput in bytes/s: 11kBytes/s
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Conclusion
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==========
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Contrary to the original USB Blaster, the cheap clone will never reach high
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transfer speeds over JTAG.
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