diff options
| author | Robert Jarzmik <robert.jarzmik@free.fr> | 2013-07-22 23:41:51 +0200 |
|---|---|---|
| committer | Spencer Oliver <spen@spen-soft.co.uk> | 2013-08-05 20:10:21 +0000 |
| commit | 9f2922aa7abb385d1fb24def91fac7eb4e2304c5 (patch) | |
| tree | 4c922c1c12913cea6435dd40bc73c27fc77a3855 /src | |
| parent | bb91c64a6094ef5884ec8d93db6f9a3393e58449 (diff) | |
jtag/drivers: usb_blaster cheap clone documentation
Add documentation about the cheap clone based on the Cypress
chip. The documentation has schematics data, and throughtput
mesures.
Change-Id: I51bf19ff9229565e178dd4c1231682bd9b4b7a8b
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Reviewed-on: http://openocd.zylin.com/1520
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Diffstat (limited to 'src')
| -rw-r--r-- | src/jtag/drivers/usb_blaster/README.CheapClone | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/src/jtag/drivers/usb_blaster/README.CheapClone b/src/jtag/drivers/usb_blaster/README.CheapClone new file mode 100644 index 00000000..983a441a --- /dev/null +++ b/src/jtag/drivers/usb_blaster/README.CheapClone @@ -0,0 +1,71 @@ +USB Blaster Cheap Clone +======================= + +The Altera USB Blaster has a cheap clone, based on : + - a Cypress CY7C68013A-56PVXC as the main chip + - a 74HC244D as the output latch + - a 24 MHz quartz + - a EEPROM 24C64BN + +The schematics (cut down to essential) is : + + /-----------------+----------------------\ + +--------------+ | | | +USB--| CY7C68013A | | +----------+ | | + | | | | 74HC244D | | | + . . | | | | | + . . \--o 1 20 o | 10 pins header | + | 47 o-- TCK --o 2 19 o---/ +-------+ | + | 46 o-- TDO --o 3 18 o-- TCK -----o 1 2 o | + | 45 o-- TMS --o 4 17 o-- TDO -----o 3 4 o | + | 44 o o 5 16 o-- TMS -----o 5 6 o | + | 43 o-- o 6 15 o o 7 8 o | + | 42 o-- o 7 14 o +--o 9 10 o | + | 41 o-- TDI --o 8 13 o-- ? | +-------+ | + . 40 o-- nOE \ o 9 12 o-- TDI --+ | + . . | o 10 11 o | + o 28 29 o | | | | + | | | +----------+ | + +--------------+ \ | + ---------------------------------------/ + +From this one can deduce that : + - the cypress emulates the Altera chip + - as the cypress pins used are 41-47, all output/input are controlled by 8051 + PortA. + - as the 8051 is clocked at 24Mhz, and because each USB byte is handled by the + 8051, assuming a 40 instruction cycles per USB packet, the maximum throughput + would be around 500 kHz. + +Pinout +====== + Port A.0: nOE (output enable of 74HC244D) + Port A.1: TDI + Port A.5: TMS + Port A.6: TDO + Port A.7: TCK + +Throughput considerations +========================= +Mesurements on a scope reveal that : + - for bitbang mode, the throughtput is 56.5 kbits/s + (as each clock transition is mesured at 17.7us) + - for byteshift mode, the throughput is 107.7 kbits/s + (as 63 bits TDI transmission is mesured in 585 us) + +Let's suppose that to upload a 32 bits value, it is necessary to : + - move from IDLE to DR-SHIFT : 3 bitbang (3 TMS transitions) + - input the 32 bits of data : 1 byteshift (24 bits) + 8 bitbang (8 bits) + - move from DR-SHIFT to IDLE : 5 bitbang (5 TMS transitions) +So for this 32 bits of data, the time would be : + 3 * 17.7us + 1 * 585us/63*24 + 5 * 17.7us + = 53.1us + 222us + 88.5us + = 363us + +Throughtput in bit/s: 32 * (1 / 363E-6) = 88000 bits/s +Throughtput in bytes/s: 11kBytes/s + +Conclusion +========== +Contrary to the original USB Blaster, the cheap clone will never reach high +transfer speeds over JTAG. |