Lpc2000

Hello,

On Monday 06 February 2006 21:01, dr_danish_ali wrote:
> Hi Dominic,
> If the clocks are unrelated / asynchronous and you rely on RTCK, then sure
> the fastest you can run the TCK at is 1/6 of the core frequency. But if you
> control the core frequency (i.e. generate it and feed it into the
> oscillator pin) and also generate TCK, I reckon that you might be able to
> push TCK up to 1/2 of the core frequency and get it through the
> synchronizer.
>
> Now I don't know how many TCK ticks it takes to issue a command over JTAG
> (or if you can take over while the CPU is held in reset all the way from
> power-on). But the MAM is fully disabled so you'll need seven core ticks
> for each FLASH memory access. I do hope that someone who knows JTAG can
> tell me "Well the scan chain is 32 bits long and a command is 4 bits long
> so you'll need at least 36 TCK, i.e. 72* core cycles to take over. And in
> that time the core has executed over 10 instructions so the potential
> trapdoor is already bolted shut". I don't know JTAG so I can't say such
> things.

You can't access the JTAG port while the device is in reset, because the LPCs 
keep the test logic in reset, too.

Test logic comes out of reset in Test-Logic-Reset. From there, you have to go 
to Shift-IR to select the SCAN_N instruction, that's 5 TCK cycles. The IR 
register is 4 bits long, but the last bit is scanned when moving out of 
Shift-IR, so you spend 3 ticks shifting bits into the IR reg. From there, you 
have to move to Shift-DR to select the EmbeddedICE scan chain. This takes 7 
TCK cycles. The SCAN_N register is 4 bits long, so you shift 3 bits. Back to 
Shift-IR to select INTEST takes 8 ticks. 3 ticks for the instruction. 7 Ticks 
back to Shift-DR. The EmbeddedICE scan chain is 38 bits long, requiring a 
shift of 37 cycles. The synchronization latches only open in Run-Test/Idle, 
so you have to move there in 5 ticks, plus one tick in R-T-I for the debug 
request to register.
5 + 3 + 7 + 3 + 8 + 3 + 7 + 37 + 5 + 1 = 79 TCK cycles.

>
> *according to my suspicion that you can push TCK up to half the core
> frequency
>
> Regards,
> Danish
>

Regards,

Dominic