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* par.c: changed order of port-read/writes in par_txrx().

Browse Source 
This change should increase immunity to delays in the
	programmer-hardware.
	Also did some unrelated cleanup in par_txrx().


git-svn-id: svn://svn.savannah.nongnu.org/avrdude/trunk/avrdude@408 81a1dc3b-b13d-400b-aceb-764788c761c2
This commit is contained in:
hinni
2004-01-29 12:57:09 +00:00
parent 3ee1be5529
commit a3e1f50cf1
2 changed files with 37 additions and 18 deletions
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48
par.c
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@@ -225,34 +225,46 @@ static unsigned char par_txrx(PROGRAMMER * pgm, unsigned char byte)
unsigned char r, b, rbyte;
rbyte = 0;
for (i=0; i<8; i++) {
b = (byte >> (7-i)) & 0x01;
for (i=7; i>=0; i--) {
/*
* Write and read one bit on SPI.
* Some notes on timing: Let T be the time it takes to do
* one par_setpin()-call resp. par clrpin()-call, then
* - SCK is high for 2T
* - SCK is low for 2T
* - MOSI setuptime is 1T
* - MOSI holdtime is 3T
* - SCK low to MISO read is 2T to 3T
* So we are within programming specs (expect for AT90S1200),
* if and only if T>t_CLCL (t_CLCL=clock period of target system).
*
* Due to the delay introduced by "IN" and "OUT"-commands,
* T is greater than 1us (more like 2us) on x86-architectures.
* So programming works safely down to 1MHz target clock.
*/
b = (byte >> i) & 0x01;
/*
* read the result bit (it is either valid from a previous clock
* pulse or it is ignored in the current context)
*/
r = par_getpin(pgm->fd, pgm->pinno[PIN_AVR_MISO]);
/* set the data input line as desired */
par_setpin(pgm->fd, pgm->pinno[PIN_AVR_MOSI], b);
/*
* pulse the clock line, clocking in the MOSI data, and clocking out
* the next result bit
*/
par_pulsepin(pgm->fd, pgm->pinno[PIN_AVR_SCK]);
rbyte = rbyte | (r << (7-i));
par_setpin(pgm->fd, pgm->pinno[PIN_AVR_SCK], 1);
/*
* read the result bit (it is either valid from a previous falling
* edge or it is ignored in the current context)
*/
r = par_getpin(pgm->fd, pgm->pinno[PIN_AVR_MISO]);
par_setpin(pgm->fd, pgm->pinno[PIN_AVR_SCK], 0);
rbyte |= r << i;
}
return rbyte;
}
static int par_rdy_led(PROGRAMMER * pgm, int value)
{
par_setpin(pgm->fd, pgm->pinno[PIN_LED_RDY], !value);