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ARM: add comments re DAP assumptions 

I think some of these assumptions are not well-founded.
Related, that swjdp_transaction_endcheck() is a bit iffy.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
__archive__
David Brownell 2010-01-05 12:55:46 -08:00
parent 9d83df72dc
commit adf2a9a267
1 changed files with 14 additions and 2 deletions
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16
src/target/arm_adi_v5.c
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@ -195,8 +195,12 @@ static int scan_inout_check_u32(struct swjdp_common *swjdp,
uint8_t instr, uint8_t reg_addr, uint8_t RnW,
uint32_t outvalue, uint32_t *invalue)
{
/* Issue the read or write */
adi_jtag_dp_scan_u32(swjdp, instr, reg_addr, RnW, outvalue, NULL, NULL);
/* For reads, collect posted value; RDBUFF has no other effect.
* Assumes read gets acked with OK/FAULT, and CTRL_STAT says "OK".
*/
if ((RnW == DPAP_READ) && (invalue != NULL))
adi_jtag_dp_scan_u32(swjdp, JTAG_DP_DPACC,
DP_RDBUFF, DPAP_READ, 0, invalue, &swjdp->ack);
@ -235,6 +239,9 @@ int swjdp_transaction_endcheck(struct swjdp_common *swjdp)
/* Why??? second time it works??? */
#endif
/* Post CTRL/STAT read; discard any previous posted read value
* but collect its ACK status.
*/
scan_inout_check_u32(swjdp, JTAG_DP_DPACC,
DP_CTRL_STAT, DPAP_READ, 0, &ctrlstat);
if ((retval = jtag_execute_queue()) != ERROR_OK)
@ -787,13 +794,18 @@ int mem_ap_read_buf_u32(struct swjdp_common *swjdp, uint8_t *buffer, int count,
DPAP_READ, 0, NULL, NULL);
for (readcount = 0; readcount < blocksize - 1; readcount++)
{
/* Scan out read instruction and scan in previous value */
/* Scan out next read; scan in posted value for the
* previous one. Assumes read is acked "OK/FAULT",
* and CTRL_STAT says that meant "OK".
*/
adi_jtag_dp_scan(swjdp, JTAG_DP_APACC, AP_REG_DRW,
DPAP_READ, 0, buffer + 4 * readcount,
&swjdp->ack);
}
/* Scan in last value */
/* Scan in last posted value; RDBUFF has no other effect,
* assuming ack is OK/FAULT and CTRL_STAT says "OK".
*/
adi_jtag_dp_scan(swjdp, JTAG_DP_DPACC, DP_RDBUFF,
DPAP_READ, 0, buffer + 4 * readcount,
&swjdp->ack);