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firmware: use the full 11 bit US_FIDI.FI_DI_RATIO

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US_FIDI_FI_DI_RATIO_Msk is 0x7ff,
cemu rejected >= 0x400 in emu_update_fidi() and masked with 0x3ff
in card_emu_uart_update_fidi(), but update_fidi() used by
the sniffer already used 0x7ff.

-> ratios 1024..2047 are unusable in cemu, which is the entire upper
half of ISO 7816-3 Table 7 at Di=1.

A reader trying one of those in a PPS gets the proposal echoed and
accepted, after which the card keeps transmitting at the old rate.

FI_DI_RATIO is clock periods per bit -> larger ratio is a SLOWER link.
The old check rejected slow values but accepted Fi=372/Di=64, ratio 5 !?

Unify and use the register mask (= shifed by 0 so usable as value) and
reject ratios that do not fit rather than truncating to garbage dividers.

Change-Id: I6211dd5be7c5c5d2150af2aa37a403b33e6d340d
This commit is contained in:
Eric Wild
2026-07-28 17:42:32 +02:00
committed by lynxis lazus
parent 889b8d8927
commit 88a6a782a2
3 changed files with 4 additions and 4 deletions
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firmware/libcommon/source/card_emu.c
+1 -1
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@@ -376,7 +376,7 @@ static void emu_update_fidi(struct card_handle *ch)
int rc;
rc = iso7816_3_compute_fd_ratio(ch->F_index, ch->D_index);
if (rc > 0 && rc < 0x400) {
if (rc > 0 && rc <= (US_FIDI_FI_DI_RATIO_Msk >> US_FIDI_FI_DI_RATIO_Pos)) {
TRACE_INFO("%u: computed F(%u)/D(%u) ratio: %d\r\n", ch->num,
ch->F_index, ch->D_index, rc);
/* make sure UART uses new F/D ratio */